Preparation method of high-strength wood-based material capable of recycling all components of waste liquid

Abstract

The invention belongs to the field of green production of structural materials and waste liquid recovery, and particularly relates to a preparation method of a high-strength wood-based material capable of recycling all components of waste liquid. The method comprises the following steps: carrying out chemical treatment on wood by utilizing an organic solvent aqueous solution to partially remove lignin and hemicellulose, and then heating and compressing to obtain the high-strength wood-based material; based on the physical property difference of an organic solvent, water and byproducts, the chemical solvent in the prepared waste liquid is recovered and recycled by a one-step physical method, and meanwhile, lignin and hemicellulose hydrolysate are obtained through separation. According to the method, the waste liquid is recycled, so that environmental pollution is reduced, meanwhile, extracted lignin and hemicellulose hydrolysate can be used for production of other industrial products, and all-component recycling of the waste liquid is realized. The preparation method is green, clean and low in cost, the obtained high-strength wood-based structural material has important application value in the fields of space flight and aviation, building traffic and the like, and the obtained by-product can be used for downstream industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of green production of structural materials and waste liquid recycling, and specifically relates to a method for preparing a high-strength wood-based material in which all components of waste liquid can be recycled. Background Art

[0002] As the most abundant natural biological resource in the world, wood is a renewable and degradable green material. However, with the continuous advancement of the modernization of industrial production, the mechanical properties of natural wood have been difficult to meet the existing engineering needs. How to prepare natural wood resources with huge reserves, green sustainability, degradability and renewable into lightweight, high-strength and high-toughness wood-based structural materials has become an important research topic for building green and environmentally friendly new structural materials. At present, although the method of pretreatment and hot pressing by inorganic chemical solution can greatly improve the strength and toughness of wood-based structural materials (see patent publication number CN110914029 A), the generated strong alkaline (strong acid) waste liquid is highly corrosive, biologically toxic and difficult to recycle, causing serious pollution to the environment. In addition, the lignin and hemicellulose hydrolyzates with high added value in the waste liquid cannot be extracted and utilized. Therefore, the prior art urgently needs a method for preparing high-strength wood-based materials that can greatly improve the strength of wood-based materials and at the same time realize the recycling of solvents and the extraction and utilization of by-products. Summary of the invention

[0003] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing high-strength wood-based materials by recycling all components of waste liquid. The mechanical properties of the wood-based materials prepared by this method are greatly improved, and the environmental cost is greatly reduced by recycling the chemical solution, thereby realizing green and clean production. The lignin and hemicellulose hydrolyzate extracted from the treatment liquid can be used for subsequent high value-added applications. The method of the present invention realizes the recycling of all components of the waste liquid, overcomes the problem that the waste liquid cannot be recycled in the traditional treatment method, and provides a new idea for the clean and green production of high-strength wood-based structural materials.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] A method for preparing a high-strength wood-based material for recycling all components of waste liquid, the specific steps are as follows:

[0006] A. Preparation of high-strength wood-based materials

[0007] Add natural wood to the chemical solution, then react under specific conditions, remove the treated wood and waste liquid after the reaction is complete. After boiling and washing the treated wood, place it in a hot press for hot pressing and densification, and obtain a high-strength wood-based material with mechanical properties far exceeding that of natural wood.

[0008] B. Separation and recovery of all components of waste liquid

[0009] Based on the differences in the physical properties of the organic solvent, water and by-products, the waste liquid obtained in step A is physically separated and recovered, the chemical solution obtained by separation and recovery is collected, and the by-products: lignin and hemicellulose hydrolyzate are extracted for subsequent high value-added applications, thereby achieving efficient full-component recycling of the waste liquid.

[0010] The chemical solution used in step A of the present invention is at least one of deionized water, methanol, ethanol, a mixed aqueous solution of ethanol and an acidic catalyst, a mixed aqueous solution of ethanol and a basic catalyst, a mixed aqueous solution of ethanol and an inorganic salt catalyst, ethylene glycol, glycerol, tetrahydrofurfuryl alcohol, butanol, formic acid, acetic acid, oxalic acid, lactic acid, maleic acid, citric acid, ethyl acetate, ether, acetone, phenol, dimethyl sulfoxide, 2-methyltetrahydrofuran, p-toluenesulfonic acid, and 5-sulfosalicylic acid, and the mass concentration range is 20% to 100%, and the liquid-to-solid ratio of the natural wood to the chemical solution is at least 2mL:1g.

[0011] The natural wood used in step A of the present invention includes at least one of common woods such as basswood, oak, poplar, ash, alder, aspen, balsa wood, beech, birch, cherry, walnut, chestnut, yellow sandalwood, elm, hickory, maple, oak, rosewood, plum, walnut, willow, boxwood, cedar, cypress, Douglas fir, fir, hemlock, larch, pine, redwood, spruce, North American larch, juniper and yew.

[0012] The specific reaction conditions in step A of the present invention are reaction temperature of 60 to 220° C. and reaction time of 0.25 to 12 hours.

[0013] In step A of the present invention, the hot pressing direction of the treated wood is perpendicular to the growth direction of the wood, and the hot pressing process conditions are hot pressing pressure of 1-50MPa, hot pressing temperature of 20-120°C, and holding time of at least 10 minutes.

[0014] The high-strength wood-based material prepared in step A of the present invention has a density of 0.8-1.5 g / cm 3 , the tensile strength is at least 200MPa.

[0015] The physical separation and recovery method of the waste liquid in step B of the present invention is at least one of fractionation, distillation, boiling, dilution precipitation, static precipitation, centrifugation, filtration and the like.

[0016] In step B of the present invention, the waste liquid is recovered by fractionation and filtering the remaining liquid, wherein the fractionation conditions are a pressure of -0.095 to -0.08 MPa, a temperature of at least 20° C., and a fractionation time of at least 20 min.

[0017] The recovery rate of the chemical solution in step B of the present invention is at least 50%, and can be used for the preparation of the next round of high-strength wood-based materials. The high-strength wood-based materials prepared by re-treating with the recovered chemical solution have no significant changes in elastic modulus, tensile strength, bending strength, fracture work, fracture toughness, density and other properties.

[0018] In the present invention, the proportion of lignin extracted in step B to the total amount of removed lignin is greater than 60%, and the extracted lignin still retains the characteristic molecular structures such as β-O-4, β-β, β-5, guaiacyl, syringyl, p-hydroxyphenyl and the like existing in natural lignin.

[0019] All substances in the hemicellulose hydrolyzate extracted in step B of the present invention are biodegradable, and its main components include furfural, xylose, mannuronic acid, trehalose, glucose, mannose, galactose, arabinose, rhamnose, glucuronic acid and oligosaccharides composed of the above monosaccharides, among which the xylose content accounts for 30-60%.

[0020] After the recovery in step B of the present invention, no waste liquid or waste is discharged except the recovered chemical solution, lignin and hemicellulose hydrolyzate.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention partially removes lignin and hemicellulose from wood through organic chemical solution pretreatment, and effectively softens the wood structure, and then realizes the preparation of high-strength wood-based materials through compression and densification. The prepared high-strength wood-based structural materials have excellent mechanical properties, which are superior to high-strength wood-based materials prepared by traditional treatment methods, and have important research value in the fields of aerospace, construction, transportation, etc.;

[0023] 2. While preparing high-strength wood-based materials, the present invention recovers chemical solutions in waste liquid by physical means such as distillation based on the difference in boiling points between the water phase and the organic solvent phase, thus overcoming the problem of difficulty in separating and recovering chemical solutions in waste liquid in traditional treatment methods.

[0024] Third, the chemical solution recovered in the present invention can be reused in the pretreatment process of wood, thereby realizing continuous multiple recycling, and the physical properties and mechanical properties of the high-strength wood-based materials prepared in multiple recycling have no obvious difference, which overcomes the problem that the chemical solution in the traditional preparation method can only be used once;

[0025] 4. While preparing high-strength wood-based materials, the present invention quickly and efficiently separates and extracts lignin and hemicellulose hydrolysate from waste liquid through distillation and other means based on the difference in solubility of by-products in water phase and organic solvent phase. The hemicellulose hydrolysate contains components such as monosaccharides and furfural. The above by-products can be used for subsequent high value-added application production, overcoming the problem that high value-added by-products in waste liquid generated by traditional methods cannot be recycled.

[0026] 5. The present invention utilizes the differences in the physical properties of organic solvents, water, lignin, and hemicellulose hydrolysates during the waste liquid recovery process to achieve rapid, physical process recovery of waste liquid without involving additional chemical processes, greatly improving the separation and recovery efficiency and avoiding potential pollution emissions caused by the chemical recovery process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the high-strength basswood material prepared in Example 1.

[0028] Figure 2 These are scanning electron microscope images of the high-strength basswood material in Example 1, wherein (a) is a scanning electron microscope image of a cross section, and (b) is a scanning electron microscope image of a side section.

[0029] Figure 3 These are the tensile test curves of the high-strength basswood material and natural basswood in Example 1.

[0030] Figure 4 This is a photo of the process of waste liquid distillation in Example 1.

[0031] Figure 5 It is the ethanol solution recovered by fractional distillation in Example 1.

[0032] Figure 6 This is the lignin obtained after extraction and drying in Example 1.

[0033] Figure 7 It is the hemicellulose hydrolyzate remaining after filtration in Example 1.

[0034] Figure 8 The two-dimensional nuclear magnetic resonance spectrum and related structure diagram of the lignin extracted in Example 1. DETAILED DESCRIPTION

[0035] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0036] Example 1

[0037] A. Preparation of high-strength basswood materials

[0038] Take 400mL of 60% ethanol solution, add 200g of natural basswood, and after the ethanol solution completely soaks the basswood, place the wood chips and solution in a reactor, heat to 190℃ in a completely closed condition and react for 5h (the pressure during the reaction is about 2MPa). Take out the treated basswood, boil and clean it, place it in a hot press, heat it to 100℃ under a pressure of 50MPa, keep this temperature and hot press for 12 hours, compact the original pores in the natural wood, and after cooling, obtain a high-strength basswood material with strength and toughness far exceeding that of natural wood ( Figure 1 , high-strength basswood block on the left, high-strength basswood slice on the right), the scanning electron microscope images of its cross section and side section are shown in Figure 2 As shown in the figure, its strength is 668MPa, which is 10 times that of natural basswood. Figure 3 ).

[0039] B. Separation and recovery of all components of waste liquid

[0040] The black waste liquid was placed in a rotary evaporator and fractionated and recovered at -0.095 MPa pressure and 40 °C for 1 hour (process as shown in Figure 4 As shown), a 72% ethanol solution ( Figure 5 ), which can be used for the next round of wood treatment. Then the remaining solution is filtered to obtain lignin precipitate (after drying, such as Figure 6 As shown) and hemicellulose hydrolysate ( Figure 7 ), thus achieving the recycling of all components of the waste liquid. According to calculations, the recovery rate of ethanol is 92%, and the tensile strength of the high-strength basswood material obtained by reprocessing with the recycled ethanol is 598MPa on average; the extraction rate of lignin is 97%, and the 2D-NMR test confirms that it has the specific structure contained in natural lignin ( Figure 8 ); The hemicellulose hydrolysate contains hemicellulose hydrolysate products such as furfural, oligosaccharides, and monosaccharides. The top three monosaccharide products are xylose (57%), mannuronic acid (14%), and fucose (11%) (see Table 1).

[0041] Table 1

[0042]

[0043] Example 2

[0044] A. Preparation of high-strength balsa wood materials

[0045] Take 300mL of 60% ethanol solution, add 20g of natural balsa wood, and after the ethanol solution completely soaks the balsa wood, place the wood and the solution in a reactor, and heat to 190℃ for 3h in a completely closed condition. Take out the treated balsa wood, boil and clean it, place it in a hot press, heat it to 100℃ under a pressure of 35MPa, and keep this temperature for 6 hours to compact and densify the original holes in the natural wood. After cooling, a high-strength balsa wood material with strength and toughness far exceeding that of natural wood is obtained. After testing, its tensile strength is 377MPa, which is about 21 times higher than that of natural balsa wood (18MPa).

[0046] B. Separation and recovery of all components of waste liquid

[0047] Add 3 times the volume of deionized water to the waste liquid obtained after ethanol treatment of balsa wood. After standing for 2 hours, lignin precipitates. After centrifugation at 5000rpm for 5 minutes, collect and extract lignin at the bottom of the container. After lignin extraction, place the remaining solution in a rotary evaporator rotating bottle, distill at -0.09MPa pressure and 40℃ for 2 hours, and obtain a 60% ethanol solution in the collection bottle, which can be used for the next round of wood treatment. The remaining solution in the rotating bottle is hemicellulose hydrolyzate, so that all components of the waste liquid are recycled.

[0048] Example 3

[0049] A. Preparation of high-strength birch wood materials

[0050] Take 300mL of 70% methanol solution, add 30g of natural birch chips, and after the methanol solution completely soaks the birch chips, place the chips and the solution in a reactor, and heat to 200℃ for 3h in a completely closed condition. Take out the treated birch chips, boil and clean them, place them in a hot press, heat to 100℃ under a pressure of 25MPa, and keep this temperature for 8 hours to compact and densify the original pores in the natural wood. After cooling, a high-strength birch material with strength and toughness far exceeding that of natural birch chips is obtained.

[0051] B. Separation and recovery of all components of waste liquid

[0052] The waste liquid was placed in the rotating bottle of the rotary evaporator and fractionated and recovered at -0.09 MPa pressure and 40°C for 0.5 hours to obtain a methanol solution with a mass fraction of 75% in the collection bottle, which can be used for the next round of wood treatment. The remaining solution in the rotating bottle was then filtered to obtain lignin precipitate and hemicellulose hydrolyzate, thus realizing the recycling of all components of the waste liquid.

[0053] Example 4

[0054] A. Preparation of high-strength basswood materials

[0055] Take 300mL of a 60% methanol-ethanol mixed aqueous solution (mass ratio of 1:1), add 60g of natural basswood chips, and after the mixed solution completely soaks the basswood chips, place the chips and the solution in a reactor, and heat to 170°C for 5h under completely closed conditions. Take out the treated basswood chips, boil and clean them, place them in a hot press, heat to 100°C at a pressure of 20MPa, and keep this temperature for 5 hours to compact and densify the original holes in the natural wood. After cooling, a high-strength basswood material with strength and toughness far exceeding that of natural basswood is obtained.

[0056] B. Separation and recovery of all components of waste liquid

[0057] The waste liquid was placed in the rotating bottle of the rotary evaporator and fractionated and recovered at -0.09 MPa pressure and 40°C for 1 hour to obtain a 60% methanol-ethanol mixed solution in the collection bottle, which can be used for the next round of wood treatment. The remaining solution in the rotating bottle was then filtered to obtain lignin precipitate and hemicellulose hydrolyzate, thus realizing the full component recovery of the waste liquid.

[0058] Example 5

[0059] A. Preparation of high-strength basswood materials

[0060] Take 300mL of 50% acidic ethanol aqueous solution (containing 1% sulfuric acid by mass), add 60g of natural basswood chips, and after the chemical solution completely soaks the basswood chips, place the chips and the solution in a reactor, and heat to 140℃ for 1h under completely closed conditions. Take out the treated basswood chips, boil and clean them, place them in a hot press, heat to 80℃ under a pressure of 30MPa, and keep this temperature for 3 hours to compact and densify the original holes in the natural wood. After cooling, a high-strength basswood material with strength and toughness far exceeding that of natural basswood is obtained.

[0061] B. Separation and recovery of all components of waste liquid

[0062] The waste liquid was placed in the rotating bottle of the rotary evaporator and fractionated and recovered at -0.09 MPa pressure and 40°C for 0.5 hours to obtain a 75% ethanol solution in the collection bottle, which can be used for the next round of wood treatment. The pH of the remaining solution in the rotating bottle was then adjusted and filtered to obtain lignin precipitate and hemicellulose hydrolyzate, thus realizing the recycling of all components of the waste liquid.

[0063] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-strength wood-based material by recycling all components of waste liquid, characterized in that: The specific steps are as follows: A. Preparation of high-strength wood-based materials Add natural wood to the chemical solution to react, and take out the treated wood and waste liquid after the reaction is completed; boil and wash the treated wood and place it in a hot press for hot pressing and densification to obtain a high-strength wood-based material with higher mechanical properties than natural wood; B. Separation and recovery of all components of waste liquid Based on the differences in the physical properties of the organic solvent, water and by-products, the waste liquid obtained in step A is physically separated and recovered, the chemical solution obtained by separation and recovery is collected, and the by-products: lignin and hemicellulose hydrolyzate are extracted for subsequent high value-added applications, thereby achieving efficient full-component recycling of the waste liquid.

2. The preparation method according to claim 1, characterized in that: The chemical solution used in step A is at least one of deionized water, methanol, ethanol, a mixed aqueous solution of ethanol and an acidic catalyst, a mixed aqueous solution of ethanol and a basic catalyst, a mixed aqueous solution of ethanol and an inorganic salt catalyst, ethylene glycol, glycerol, tetrahydrofurfuryl alcohol, butanol, formic acid, acetic acid, oxalic acid, lactic acid, maleic acid, citric acid, ethyl acetate, ether, acetone, phenol, dimethyl sulfoxide, 2-methyltetrahydrofuran, p-toluenesulfonic acid, and 5-sulfosalicylic acid, and the mass concentration range is 20% to 100%, and the liquid-to-solid ratio of the natural wood to the chemical solution is at least 2mL:1g.

3. The preparation method according to claim 1, characterized in that: The natural wood used in step A includes at least one of basswood, oak, poplar, ash, alder, aspen, balsa wood, beech, birch, cherry, walnut, chestnut, rosewood, elm, hickory, maple, oak, rosewood, plum, walnut, willow, boxwood, cedar, cypress, Douglas fir, fir, hemlock, larch, pine, redwood, spruce, larch, juniper and yew.

4. The preparation method according to claim 1, characterized in that: The reaction conditions in step A are reaction temperature of 60 to 220° C. and reaction time of 0.25 to 12 hours.

5. The preparation method according to claim 1, characterized in that: In step A, the hot pressing direction of the treated wood is perpendicular to the growth direction of the wood, and the hot pressing process conditions are hot pressing pressure of 1-50MPa, hot pressing temperature of 20-120°C, and holding time of at least 10 minutes.

6. The preparation method according to claim 1, characterized in that: The high-strength wood-based material prepared in step A has a density of 0.8-1.5 g / cm 3 , the tensile strength is at least 200MPa.

7. The preparation method according to claim 1, characterized in that: The physical separation and recovery method of the waste liquid in step B is at least one of fractionation, distillation, boiling, dilution precipitation, static precipitation, centrifugation and filtration operations.

8. The preparation method according to claim 7, characterized in that: In step B, the physical separation and recovery method of the waste liquid is fractionation and filtering of the remaining liquid, wherein the fractionation conditions are a pressure of -0.095 to -0.08 MPa, a temperature of at least 20° C., and a fractionation time of at least 20 min.

9. The preparation method according to claim 1, characterized in that: The recovery rate of the chemical solution in step B is at least 50%, which is used for the preparation of the next round of high-strength wood-based materials, and the elastic modulus, tensile strength, bending strength, fracture work, fracture toughness and density of the high-strength wood-based material prepared by re-treatment with the recovered chemical solution have no obvious changes.

10. The preparation method according to claim 1, characterized in that: The proportion of lignin extracted in step B to the total amount of removed lignin is greater than 60%, and the extracted lignin still retains the characteristic molecular structures of β-O-4, β-β, β-5, guaiacyl, syringyl, and p-hydroxyphenyl present in natural lignin; the solutes of the hemicellulose hydrolyzate extracted in step B are all biodegradable, and its main components include furfural, xylose, mannuronic acid, trehalose, glucose, mannose, galactose, arabinose, rhamnose, glucuronic acid and oligosaccharides composed of the above monosaccharides, among which the xylose content accounts for 30-60%.

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