JP2022103080A - Method for decolorizing lignin, and method for preparing decolorized lignin - Google Patents

Abstract

To provide a method for decolorizing lignin that decolorizes lignin to the extent that it can be applied to various uses.SOLUTION: A method for decolorizing lignin includes reacting a plant or a processed plant containing lignin of 10-50 mass% with a compound represented by one of the general formulae (11)-(13). General formula (11) R-N=C=O, general formula (12) R-COOH, and general formula (13) R-OH (where, R is an alkyl group, an aralkyl group, an aryl group, a halogenated alkyl group, a halogenated aryl group, a sulfonyl group, or a silyl group).SELECTED DRAWING: None

Description

The present invention relates to a method for bleaching lignin and a method for preparing bleached lignin.

More than 90% of wood is composed of cell wall components, and the cell walls are mainly composed of cellulose, hemicellulose, and lignin. Of the main components, lignin is usually present in wood in an amount of about 20 to 30%, and the cell membranes are adhered to each other to form an intermediate layer. Some of the lignin in wood is also present in the cell membrane.
Lignin is a polymer compound produced by condensation with hydroxyphenylpropane as a basic unit. Lignin is π-conjugated and has an aromatic backbone structure and a phenolic hydroxyl group that can be an organic radical. Lignin having such a structure has functions as a heat-resistant filler, an ultraviolet absorber, and an antioxidant, and is expected to be used as a high-performance resin material such as engineering plastics. In addition, plant-derived polymer compounds such as lignin are also expected to function as environmentally-circulating materials.

However, common lignin is colored brown or black. Therefore, the use of lignin is limited because it causes a color change of the medium to which lignin is added and the light transmittance of the medium to which lignin is added is low.
Therefore, the lignin decolorization method is a very important technique from the viewpoint of expanding the application of lignin to material applications.

As a method for decolorizing lignin, a method for biologically decolorizing using a microorganism or an enzyme belonging to the genus Azotobacter has been proposed in Patent Document 1.
However, the microorganism used in the method described in Patent Document 1 is a microorganism that contributes to the decomposition of lignin in plants. Therefore, what is actually happening by the method described in Patent Document 1 is the decolorization of plants due to the decomposition of lignin. Therefore, it is difficult for the method described in Patent Document 1 to utilize the usefulness of lignin and expand its application to various material applications.

Furthermore, there is a technology to improve the heat resistance and hardness of the resin, compatibility with other components, etc. by modifying the hydroxyl groups (hydroxyl groups of guaiacol structure and alcoholic hydroxyl groups) of lignin obtained from pulp waste liquid by a chemical method. It has been reported (see Non-Patent Document 1).
However, lignin obtained from pulp waste liquid has unstable properties due to denaturation at the time of extraction, and it is difficult to use it as a material. In addition, since harmful chemicals such as strong acids and strong alkalis are used and heating is performed during extraction, the environmental load is large and industrial development is difficult. Furthermore, there is no report on a technique for decolorizing and whitening lignin by modifying the hydroxyl group of lignin.

Japanese Unexamined Patent Publication No. 9-67785

Green Chem., 2016, vol. 18, p. 1175-1200

As mentioned above, lignin is expected as a functional substance, but the coloring of lignin itself limits the applications to which lignin can be applied.
Therefore, it is an object of the present invention to provide a method for decolorizing lignin, which decolorizes lignin to the extent that it can be applied to various uses.
Another object of the present invention is to provide a method for preparing a decolorized lignin, which can prepare a decolorized lignin applicable to various uses.

In view of the above problems, the present inventors have repeatedly studied a method for decolorizing colored lignin. So far, it has been speculated that lignin is colored because the vinyl group at the para-position of the phenolic hydroxyl group has lost its electron conjugation and the presence of an ultraviolet chromophore.
As a result of repeated studies by the present inventors, the degree of coloration of lignin is increased by reacting a plant or a processed plant product containing a predetermined amount of lignin with a reactive compound such as an isocyanate compound and modifying the hydroxyl group of lignin. We have found that reduced and bleached lignin can be prepared (extracted).
The present invention has been completed based on these findings.

The above-mentioned problems of the present invention have been solved by the following means.
(1) A method for decolorizing lignin, which comprises reacting a plant or a processed plant product containing 10 to 50% by mass of lignin with a compound represented by any one of the following general formulas (11) to (13).
RN = C = O General formula (11)
R-COOH general formula (12)
R-OH general formula (13)
(In the general formulas (11) to (13), R represents an alkyl group, an aralkyl group, an aryl group, an alkyl halide group, an aryl halide group, a sulfonyl group, or a silyl group.)

(2) A plant or a processed plant product containing 10 to 50% by mass of lignin is reacted with a compound represented by any one of the general formulas (11) to (13) to obtain bleached lignin. How to prepare bleached lignin.

(3) The compound represented by any one of the general formulas (11) to (13) is the isocyanate compound represented by the following general formula (21), according to the above (1) or (2). the method of.

R'-N = C = O General formula (21)

(In the general formula (21), R'represents an alkyl group, an aralkyl group, or an aryl group.)
(4) The method according to any one of (1) to (3) above, wherein the obtained decolorized lignin is in the form of powder.
(5) The plants are cedar ( Cryptomeria japonica ), beech ( Fagus crenata Blume), pine genus ( Pinus ) plant, balsa ( Ochroma lagopus ), parrot's feather ( Myriophyllum aquaticum ), moso bamboo ( Phyllostachys heterocycla ), rice ( Oryza ). , Pankomugi ( Triticum aestivum ), Corn ( Zea mays subsp. Mays (L.) Iltis), Erianthus arundinaceus , Miscanthus sinensis , Saccharum officinarum , Yoshi ( Phragmites australis ) Arundo donax , oil palm, Elaeis , Nypa fruticans Wurmb , Arenga pinnata or Arenga saccharifera , Eichhornia crassipes , Potamogeton maackianus , Potamogeton maackianus ), Elodea nuttallii , Sargassum horneri , Sargassum fulvellum , Ulva , Caulerpa taxifolia , Caulerpa lentillifera , and Eucheuma . The method according to any one of (1) to (4) above, which is at least one kind of plant.
(6) The plant-treated product is chipper-treated, dry-crushed, wet-crushed, grinded, saccharified, fermented, digested, crushed, subcritical water-treated, decomposed with ionic liquid, acid-treated, The method according to any one of (1) to (5) above, wherein at least one treatment selected from the group consisting of base treatment and microwave treatment is performed.

According to the present invention, colored lignin can be decolorized, and decolorized lignin can be produced. The decolorized lignin that can be obtained by the present invention is applied as a functional substance to various media such as resin compositions, polymer materials, coating materials, cosmetic compositions, automobile parts, building materials, adhesives, and heat-resistant fillers. can do.

It is a figure which shows the FT-IR spectrum of the lignin prepared in Examples 1 and 2. It is a figure which shows the ultraviolet-visible absorption spectrum of the lignin prepared in Example 1. FIG. It is the thermogravimetric measurement result of the polyipcilon caprolactam (PCL + lignin) containing the lignin prepared in Example 2 and the polyipcilon caprolactam (PCL) alone.

In the present invention, a plant or a processed plant product containing 10 to 50% by mass of lignin (hereinafter, also referred to as "plant raw material") is reacted with a specific compound having a reactive functional group for the hydroxyl group of lignin, and these are reacted. By modifying the hydroxyl group, the colored lignin is decolorized.
Hereinafter, the present invention will be described based on a preferred embodiment. However, the present invention is not limited to these.

The lignin to be treated in the present invention is a polymer compound present in the cell wall or cell membrane of a plant. Lignin is composed of hydroxyphenylpropane as a basic unit. Lignin differs in the type and composition of the substituted aromatic substance, which is a constituent unit thereof, depending on the plant species such as conifers, hardwoods, and gramineous plants. The lignin used as a treatment target in the present invention may be obtained from any plant as long as it contains a predetermined amount of lignin.
Further, in the present invention, the treatment target is not particularly limited as long as it contains a predetermined amount of lignin, and may contain components constituting cell walls and cell membranes such as cellulose and hemicellulose.

In the method of the present invention, a plant or a processed plant product containing 10 to 50% by mass of lignin is used as a starting material to be reacted with a compound described later.
Hereinafter, the starting material used in the present invention will be described in detail.

For plants containing a predetermined amount of lignin, the amount of lignin can be quantified according to the method described below, and the plant raw material containing the predetermined amount can be used as the plant used in the present invention. Alternatively, refer to "Latest Trends in Lignin Utilization" by Shiro Saka et al. (2013), supervised by Shiro Saka, Chapter 1 "Biomass Classification and Chemical Composition", etc., and appropriately select plant raw materials containing a predetermined amount and use them in the present invention. You can also do it. Specific examples of plants containing a predetermined amount of lignin that can be used in the present invention include sugar cane, beech, bagasse, bagasse, sugar cane, sugar cane, rice (preferably grass, rice husk), bread wheat, corn, and Erianthus. , Miscanthus, sugar cane (preferably bagasse, residue after sugar cane juice), yoshi, giant reed, abra palm, nippa palm, sugar cane, hoteiaoi, senninmo, corn, kuromo, konakadamo, akamoku, hondawara, aosa Examples include sea grapes and giraffe plants, of which bagasse, beech, pine, bagasse, maize, rice, bread wheat, corn, erianthus, miscanthus, sugar cane, yoshi, giant reed, abra palm, nippa palm, and sugar cane. , Lignin content is high and can be preferably used in the present invention.
As the raw material of the plant used in the present invention, any part of the plant can be used, and the whole plant, root, mass root, rhizome, stem, branch, stem, leaf (leaf blade, peduncle, etc.), bark, sap, etc. Resins, flowers (petals, ovary, etc.), fruits, seeds, etc. can be used. Moreover, you may use a plurality of these parts in combination. Of these sites, it is preferable to use the rhizome, stem, branch, stem, leaf (leaf blade, petiole, etc.) and bark of the plant.

In the present invention, the above-mentioned plant may be used as it is, or a plant-treated product obtained by subjecting the plant to a predetermined treatment may be used. By applying the predetermined treatment to the plant, the reactivity with the compound described later can be improved and the amount of lignin contained in the plant raw material can be increased.
As the treatment applied to the plant, refer to "Latest Trends in Lignin Utilization" by Shiro Saka et al. (2013), supervised by Shiro Saka, Chapter 1 "Biomass Classification and Chemical Composition", as long as the effect of the present invention is not impaired. It can be selected as appropriate. For example, chipper treatment, dry crushing treatment, wet crushing treatment, grinding treatment, saccharification treatment, fermentation treatment, cooking treatment, blasting treatment, sub-critical water treatment, decomposition treatment with ionic liquid, acid treatment, base treatment and microwave treatment. Can be mentioned. Of these, saccharification treatment using cellulase or the like (monosaccharification treatment or low saccharification treatment) or fermentation treatment using yeast for alcohol fermentation is preferable.

When using a natural plant as a starting material in the present invention, refer to "Latest Trends in Lignin Utilization" by Shiro Saka et al. (2013), supervised by Shiro Saka, Chapter 1, "Classification and Chemical Composition of Biomass", etc. The amount can be determined. Alternatively, it is also possible to measure the amount of lignin contained in the treated product that has been subjected to a predetermined treatment by the method shown in Examples described later.

Lignin is said to have an ultraviolet chromophore because the vinyl group at the para-position of the phenolic hydroxyl group loses electron conjugation in the skeleton of aromatic compound residues (Green Chem., 2016, vol. 18, p. 1175-1200; Keiji Takabe (2013) "Latest Trends in Lignin Utilization", supervised by Shiro Saka, see Chapter 2, "Lignin Distribution and Structural Diversity in Phenolic Cells"). Since such an ultraviolet chromophore exists in lignin, it is presumed that it is colored brown or black. Therefore, it was considered that decolorization can be achieved by modifying the hydroxyl group of lignin with an organic side chain via a covalent bond and encapsulating the ultraviolet chromophore of lignin.
Therefore, in the present invention, lignin is reacted with a compound represented by any one of the following general formulas (11) to (13) (hereinafter, also simply referred to as “reactive compound”) to chemically chemically the hydroxyl group of lignin. To qualify.

RN = C = O General formula (11)
R-COOH general formula (12)
R-OH general formula (13)

In the general formulas (11) to (13), R represents an alkyl group, an aralkyl group, an aryl group, an alkyl halide group, an aryl halide group, a sulfonyl group and a silyl group.

Although the details of the mechanism by which lignin is decolorized by the present invention are not clear, the following can be considered. That is, the modification of the phenolic hydroxyl group causes the restoration of electron conjugation and inhibits the π-π interaction of the aromatic ring of lignin. In addition, an organic side chain chemically modified via the hydroxyl group of lignin covers the ultraviolet chromophore of lignin. As a result, it can be inferred that the light absorption by lignin is suppressed and the lignin is decolorized.
The reactive compound used in the present invention may be used alone or in combination of two or more.

In the general formula (11), R represents an alkyl group, an aralkyl group, an aryl group, an alkyl halide group, an aryl halide group, a sulfonyl group and a silyl group. Of these, R is preferably an alkyl group, an aralkyl group or an aryl group from the viewpoint of solubility of the reaction product in an organic solvent, an alkyl group having 2 to 18 carbon atoms, an aralkyl group having 7 to 24 carbon atoms or an aralkyl group having 7 to 24 carbon atoms. An aryl group having 7 to 24 carbon atoms is preferable, an alkyl group having 6 to 12 carbon atoms, an aralkyl group having 7 to 18 carbon atoms, or an aryl group having 7 to 18 carbon atoms is more preferable.
Specific examples of the reactive compound (isocyanate compound) represented by the general formula (11) include ethyl isocyanate, propyl isocyanate, butyl isocyanate, pentyl isocyanate, hexyl isocyanate, hexyl diisocyanate, heptyl isocyanate, octyl isocyanate, decyl isocyanate and dodecyl. Alkyl isocyanate such as isocyanate, tetradecyl isocyanate, octadecyl isocyanate, benzyl isocyanate, phenethyl isocyanate, 1,3-bis (2-isocyanato-2-propyl) benzene, naphthylethyl isocyanate, methylbenzyl isocyanate, 3-isopropyl-α, α -Aralkyl isocyanate such as dimethylbenzyl isocyanate, tosyl isocyanate, xylenediisocyanate, phenylisocyanate, phenylenediocyanate, dimethylphenylisocyanate, ethoxyphenylisocyanate, acetylphenylisocyanate, butylphenylisocyanate, diisopropylphenylisocyanate, naphthylisocyanate, nitrophenylisocyanate, biphenylisocyanate , Tosyl-2,6-diisocyanate, 4-ethylphenylisocyanate, methoxyphenylisocyanate, naphthalin-1,5-diisocyanate, arylisocyanate such as 2-methoxyphenylisocyanate, halogen such as chloropropylisocyanate and trichloroacetylisocyanate. Alkyl isocyanate, chlorophenyl isocyanate, bromophenylisocyanate, dichlorophenylisocyanate, trichlorophenylisocyanate, chloromethylphenylisocyanate, chloronitrophenylisocyanate, fluorophenylisocyanate, difluorophenylisocyanate, trifluoromethylphenylisocyanate, trifluoromethoxyphenylisocyanate, bis ( Examples thereof include halogenated aryl isocyanates such as trifluoromethyl) phenyl isocyanate and chloro (trifluoromethyl) phenyl isocyanate, sulfonyl isocyanates such as chlorosulfonyl isocyanate, benzyl sulfonyl isocyanate and toluene sulfonyl isocyanate, and silyl isocyanates such as trimethylsilyl isocyanate. Of these, alkyl isocyanates, aralkyl isocyanates or aryl isocyanates are preferable, and hexyl isocyanates, hexyl diisocyanates, heptyl isocyanates, octadecyl isocyanates, dodecyl isocyanates, benzyl isocyanates, phenethyl isocyanates and diisopropylphenyl isocyanates are more preferable.

R in the general formula (12) is synonymous with R in the general formula (11), and the preferred range is also the same.
Specific examples of the reactive compound (carboxylic acid) used in the general formula (12) include propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, and tetradecanoic acid. Hexadecanoic acid, heptadecanoic acid, octadecanoic acid, 3- (2-amino-2-oxoethyl) -5-methylhexane, 5-azidopentanoic acid, crotonic acid, cyanoacetic acid, aminocinamic acid, atrolactic acid, (aminomethyl) phenyl Acetic acid, 2-phenylacrylic acid, 3-aminocapacic acid, benzoic acid, 2-amino-4,5-dimethylbenzoic acid, anthracenecarboxylic acid, 3-chloropropionic acid, 5-chloropentanoic acid, 2,3- Dichloroisobutyric acid, 3-bromopropionic acid, 3-bromo-2-oxopropionic acid, 2-bromoisobutyric acid, 9-bromononanoic acid, 2,3-dibromopropionic acid, 3-iodopropionic acid, 3-amino-3-( 4-Chlorophenyl) propionic acid, 2-acetamide-5-bromobenzoic acid, 4- (bromomethyl) phenylacetic acid, 4-bromosilky acid, 4- (2-bromoethyl) benzoic acid, 2- (p-toluenesulfonyl) Examples include acetic acid and 3- (trimethylsilyl) propiole acid. Of these, caproic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanic acid, octanoic acid, nonanoic acid, decanoic acid, and dodecanoic acid are preferable.

R in the general formula (13) is synonymous with R in the general formula (11), and the preferred range is also the same.
Specific examples of the reactive compound (alcohol) used in the general formula (13) include ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, dodecanol, tetradecanol, hexadecanol, and heptadeca. Nord, octadecanol, docosanol, icosanol, benzyloxypropanol, cinnamyl alcohol, cyclohexylpropanol, phenoxypropanol (chloro-iodo) bromoethanol, (chloro) bromopropanol, (chloro) bromopentanol, (chloro) bromoexanol , Bromoundecyl alcohol, bromodecanol, 2-[(3-aminophenyl) sulfonyl] ethanol. Of these, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and dodecanol are preferable.

In the present invention, the reactive compound is preferably an isocyanate compound represented by the following general formula (21).

R'-N = C = O General formula (21)

In the general formula (21), R'represents an alkyl group, an aralkyl group, or an aryl group. The alkyl group, aralkyl group and aryl group represented by R'have the same meaning as the alkyl group, aralkyl group and aryl group represented by R in the general formulas (11) to (13), respectively, and the preferable range is also the same.

The method for modifying the hydroxyl group of lignin is not particularly limited. For example, when modifying a phenolic hydroxyl group, a modification method in which the electron conjugation of the vinyl group is restored and the π-π interaction of the aromatic ring of lignin is inhibited is preferable. In the present invention, the reaction of lignin with a reactive compound forms at least one bond selected from the group consisting of urethane bonds, ester bonds and ether bonds.
The formation of urethane bonds, ester bonds and ether bonds in the present invention will be described in detail based on the general formulas (1) to (3) shown below. Lignin is a huge polymer compound that forms a complicated structure by highly polymerizing by a random radical coupling reaction. Therefore, the structure of lignin has not yet been clearly elucidated. Therefore, in the present specification, when expressing the chemical structure of lignin, only the guaiacol structure and the vinyl group at the para-position of the phenolic hydroxyl group are described in detail, and the other parts are omitted or simplified. Furthermore, in actual lignin, a substituent is bonded to the vinyl group at the para position of the phenolic hydroxyl group to form a complex aromatic backbone structure as a whole. However, in the present specification, the bond of such a substituent to the vinyl group is also omitted. Further, the substituent bonded to the vinyl group may have an alcoholic hydroxyl group. The description of such an alcoholic hydroxyl group is also omitted.
In this specification, the chemical structure of lignin is expressed by focusing on one guaiacol structure among the lignins forming a complicated aromatic main chain structure. Therefore, when the reactive compound used in the present invention has two or more reactive functional groups in the molecule, one reactive functional group reacts with the phenolic hydroxyl group, and the remaining reactive functional groups remain unreacted. It is described for convenience. However, since lignin has many phenolic hydroxyl groups and alcoholic hydroxyl groups, the remaining reactive functional groups are not in an unreacted state, but react with other phenolic hydroxyl groups and alcoholic hydroxyl groups, resulting in a complicated structure. It is formed.

The general formula (1) shows a reaction formula when the reactive compound represented by the general formula (11) is used. In the general formula (1), a urethane bond is formed by an addition reaction between a hydroxyl group having a guaiacol structure of lignin and an isocyanate compound. For alcoholic hydroxyl groups not represented by the general formula (1), urethane bonds are formed by an addition reaction with the reactive compound represented by the general formula (11).

The general formula (2) shows a reaction formula when the reactive compound represented by the general formula (12) is used. In the general formula (2), an ester bond is formed by a condensation reaction between a hydroxyl group having a guaiacol structure of lignin and a carboxylic acid. Even for alcoholic hydroxyl groups not represented by the general formula (2), an ester bond is formed by a condensation reaction with the reactive compound represented by the general formula (12).

The general formula (3) shows a reaction formula when the reactive compound represented by the general formula (13) is used. In the general formula (3), an ether bond is formed by a condensation reaction between a hydroxyl group having a guaiacol structure of lignin and an alcohol. For alcoholic hydroxyl groups not represented by the general formula (3), an ether bond is formed by a condensation reaction with the reactive compound represented by the general formula (13).

The structure of lignin after the reaction between lignin and the reactive compound is specifically shown below. However, the present invention is not limited to these.

The reaction conditions for modifying the hydroxyl group of lignin are not particularly limited, and the conditions carried out by a conventional method can be appropriately selected.
For example, a solvent is appropriately selected from water, ethanol, methanol, isopropanol, alcohol such as n-butanol, carboxylic acid such as formic acid and acetic acid, dimethyl sulfoxide, acetonitrile, dimethylformamide, N-methylpyrrolidone and the like, and in the selected solvent. , The plant material and the reactive compound are mixed. The solvent of the reaction system used in the present invention is preferably water, ethanol or a mixture thereof from the viewpoint of solubility. The mixing ratio of the plant raw material and the reactive compound can also be appropriately selected, and the reactive compound having a stoichiometric equimolar or more with respect to the hydroxyl group of lignin contained in the plant raw material is mixed with the plant raw material. Is preferable. For example, it is preferable to mix an equal amount to 9 times the mass ratio of the reactive compound with the plant material with the plant material.

After mixing the plant material and the reactive compound, the mixture may be allowed to stand to react the lignin with the reactive compound, but it is preferable to stir the mixture to react the lignin with the reactive compound. The reaction temperature is preferably 20 to 150 ° C, more preferably 20 to 60 ° C. The reaction time is preferably 3 to 24 hours, more preferably 3 to 5 hours.

The reaction between the plant material and the reactive compound can be terminated by adding an excess amount of solvent to the reaction system. After the chemical reaction, the unreacted product can be removed from the product according to a conventional method such as filter filtration or column chromatography to separate and purify the decolorized lignin. The solvent used for separation and purification of the reaction product is not particularly limited, but it is preferable to use an alcohol solvent such as ethanol in order to maintain the degree of decolorization of the reaction product. Further, by removing the solvent of the reaction system by a conventional method after the chemical reaction, powdery decolorized lignin can be obtained.

By going through the above steps, bleached lignin can be obtained. As used herein, the term "bleaching" means that the degree of coloring of lignin is reduced, and the decolorization of lignin can be confirmed by visually observing the measuring device for the degree of coloring and the appearance.

Since lignin is applied to various media such as resin compositions, polymer materials, coating materials, cosmetic compositions, automobile parts, building materials, adhesives, and heat-resistant fillers, the white color of lignin obtained by the method of the present invention is used. The degree is preferably high, and white lignin having an L * value of 80 or more in the L * a * b * color space is more preferable. The L * a * b * color space is a kind of complementary color space, which has a dimension L * indicating lightness and complementary color dimensions a * and b *, and is based on a non-linear compression of the coordinates of the CIE XYZ color space. There is. As used herein, "white" is defined as having an L * value of 80 or more in the L * a * b * color space. L * value, a * value, and b * value can be measured according to JIS Z 8781-4: 2013.
The whiteness (L * value) of lignin can be adjusted by appropriately selecting a plant material, a reactive compound, a reaction solvent, a reaction temperature / time, and a method for separating / purifying the reaction product. For example, when a plant raw material is prepared from wood or the like, a reaction in which a base and sulfur coexist is performed, and therefore, when the raw material contains these components or a color-developing group generated by a chemical reaction induced by these components, the reaction product is produced. The degree of bleaching may decrease and the desired L * value may not be achieved. In this case, it is preferable to remove components such as bases and sulfur from the plant raw materials.

Further, a transparent film containing lignin can be produced by applying the decolorized lignin solution obtained in the present invention to an appropriate support such as a PET plate or a glass plate and drying the solution. Further, the decolorizing lignin obtained in the present invention has functions such as a heat-resistant filler and an adhesive. Therefore, by blending the decolorizing lignin obtained in the present invention with a medium such as a resin composition, a polymer material, a coating material, a cosmetic composition, an automobile member, or a building material, the medium does not cause a change in the original color. , The function of lignin can be imparted to the medium.
In the present invention, the solvent for preparing the lignin solution is not particularly limited, and can be appropriately selected according to the physical characteristics of the reactive compound used in the present invention. Specific examples include ethanol, acetone, chloroform, acetamide, acetonitrile, isopropanol, 1,4-dioxane, dimethyl sulfoxide, tetrahydrofuran, toluene, nitrobenzene, hexane, methanol and the like.

The reaction carried out by the method of the present invention is carried out under mild reaction conditions as compared with the existing technique of performing a cooking treatment using a strong acid / strong base under high temperature and high pressure. Therefore, along with the decolorization and whitening of lignin, the component denaturation of lignin is suppressed. Therefore, the lignin obtained by the method of the present invention is promoted to be used as various materials as compared with the lignin obtained by the conventional method.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

Example 1
<Preparation of Sugi sawdust dispersion>
Sugi sawdust (obtained from Daisou Co., Ltd.) 0.6 g was mixed with 9.4 mL of ultrapure water and 10 mL of ethanol so as to be 3 wt% to prepare a Sugi sawdust dispersion.

<Formation of urethane bond>
To 20 mL of the obtained dispersion, 2 mL of hexyl isocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise, and the mixture was stirred at 50 ° C. and 1 atm for 5 hours to carry out a urethane bond forming reaction.
Then, an excess amount of ethanol is added to wash the mixture, the precipitate (unreacted sawdust) is decanted, and then the unreacted material (unreacted isocyanate, etc.) is removed by filter filtration and dried. The white powder was recovered.

Sugi sawdust before the urethane bond formation reaction was colored. By performing a urethane bond forming reaction on this Sugi sawdust using hexyl isocyanate, the colored Sugi sawdust (lignin) was whitened. Further, when 0.05 g of the obtained powder (lignin) was added to 1 mL each of chloroform and ethanol, the powder (lignin) was dissolved in all of these organic solvents.

Example 2
A powder was prepared in the same manner as in Example 1 except that the urethane bond forming reaction was carried out using dodecyl isocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) instead of hexyl isocyanate. As a result, the obtained powder (lignin) was whitened. Further, when 0.05 g of the obtained powder (lignin) was added to 1 mL each of chloroform and ethanol, the powder (lignin) was dissolved in all of these organic solvents.

Example 3
<Preparation of saccharified residue of Sugi wood flour>
2 kg of Sugi wood powder with a diameter of about 0.7 mm prepared by crushing with a chopper mill and a hammer mill was dispersed in water (18 L) so as to be 10% by weight. The obtained sample was wet pulverized for 6 hours with a wet bead mill (LME4; manufactured by Ashizawa Finetech) containing 2 mm zirconia beads.
A saccharifying enzyme (cellulase, GODO-TCF; manufactured by Godo Shusei Co., Ltd.) was added to the obtained slurry-like sample so that the concentration with respect to the plant was 0.2 mL / g, and the enzyme saccharification treatment was performed at 50 ° C. for 24 hours. .. Further, an enzyme for alcohol fermentation (dried yeast for sake, model number: 901 yeast, source: Kyokai yeast) was added, and parallel double fermentation was carried out at 30 ° C. for 5 days.
The obtained slurry-like sample was centrifuged at 9000 rpm for 10 minutes, and the precipitate was recovered as a saccharified residue (lignin-polysaccharide complex).

See Shiro Saka et al. (2013) "Latest Trends in Lignin Utilization", supervised by Shiro Saka, Chapter 1 "Biomass Classification and Chemical Composition". It has been. From the HPLC (LC-20AD; manufactured by Shimadzu Corporation) analysis of the centrifugation supernatant of the saccharified residue, 745 g of polysaccharide was released from the raw material Sugi wood flour. Therefore, it was identified that the above-mentioned saccharified residue contained 593 g of polysaccharide and 662 g of lignin (54% by mass by weight).

<Formation of urethane bond>
A powder was prepared in the same manner as in Example 1 except that the obtained saccharified residue was used. As a result, the obtained powder (lignin) was whitened. Further, when 0.05 g of the obtained powder (lignin) was added to 1 mL each of chloroform and ethanol, the powder (lignin) was dissolved in all of these organic solvents.

Example 4
A powder was prepared in the same manner as in Example 3 except that the urethane bond forming reaction was carried out using dodecyl isocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) instead of hexyl isocyanate. As a result, the obtained powder (lignin) was whitened. Further, when 0.05 g of the obtained powder (lignin) was added to 1 mL each of chloroform and ethanol, the powder (lignin) was dissolved in all of these organic solvents.

Example 5
<Preparation of beech sawdust dispersion>
Beech sawdust (obtained from Toei Kagaku Sangyo Co., Ltd.) 0.6 g was mixed with 9.4 mL of ultrapure water and 10 mL of ethanol so as to be 3 wt% to prepare a beech sawdust dispersion.

<Formation of urethane bond>
To 20 mL of the obtained dispersion, 2 mL of dodecyl isocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise, and the mixture was stirred at 50 ° C. and 1 atm for 5 hours to carry out a urethane bond forming reaction.
Then, an excess amount of ethanol is added to wash the mixture, the precipitate (unreacted beech waste) is decanted, and then the unreacted material (unreacted isocyanate, etc.) is removed by filter filtration and dried. The white powder was recovered.

The beech sawdust before the urethane bond formation reaction was colored. By performing a urethane bond forming reaction on the beech sawdust using dodecyl isocyanate, the colored beech sawdust (lignin) was whitened. Further, when 0.05 g of the obtained powder (lignin) was added to 1 mL each of chloroform and ethanol, the powder (lignin) was dissolved in all of these organic solvents.

Example 6
<Preparation of pine powder dispersion>
A piece of pine wood (obtained from Monotaro Co., Ltd.) was shaved with a belt and disc sander equipped with a 60-mesh file (obtained from Sankyo Corporation) to prepare 0.03 g of pine powder.
0.03 g of the prepared pine powder was mixed with 5 mL of ultrapure water and 5 mL of ethanol so as to have a concentration of 0.3 wt% to prepare a pine powder dispersion.

<Formation of urethane bond>
0.2 mL of dodecyl isocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to 10 mL of the obtained dispersion, and the mixture was stirred at 50 ° C. and 1 atm for 5 hours to carry out a urethane bond forming reaction.
Then, an excess amount of ethanol is added to wash the mixture, the precipitate (unreacted pine powder) is decanted, and then the unreacted material (unreacted isocyanato, etc.) is removed by filter filtration and dried. The white powder was recovered.

The pine powder before the urethane bond formation reaction was colored. By performing a urethane bond forming reaction on this pine powder using dodecyl isocyanate, the colored pine powder (lignin) was whitened. Further, when 0.05 g of the obtained powder (lignin) was added to 1 mL each of chloroform and ethanol, the powder (lignin) was dissolved in all of these organic solvents.

Example 7
<Preparation of Barcelona powder dispersion>
A piece of balsa (obtained from Monotaro Co., Ltd.) was scraped with a dust suction sander equipped with an 80-mesh file (obtained from Kogi Co., Ltd.) to prepare 1.00 g of balsa powder.
0.3 g of the prepared balsa powder was mixed with 10 mL of ultrapure water and 10 mL of ethanol so as to be 3 wt% to prepare a balsa powder dispersion.

<Formation of urethane bond>
To 20 mL of the obtained dispersion, 0.6 mL of dodecyl isocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise, and the mixture was stirred at 50 ° C. and 1 atm for 5 hours to carry out a urethane bond forming reaction.
Then, an excess amount of ethanol is added to wash the mixture, the precipitate (unreacted balsa powder) is decanted, and then the unreacted material (unreacted isocyanato, etc.) is removed by filter filtration and dried. The white powder was recovered.

The barcelona powder before the urethane bond formation reaction was colored. By performing a urethane bond forming reaction on this balsa powder using dodecyl isocyanate, the colored balsa powder (lignin) was whitened. Further, when 0.05 g of the obtained powder (lignin) was added to 1 mL each of chloroform and ethanol, the powder (lignin) was dissolved in all of these organic solvents.

<Test Example 1>
The color difference and color space between the powders prepared in Examples 1 to 7 and the starting material before urethane bond formation were L * a * b * in reflection mode using a Konica Minolta spectrocolorimeter (CR-5). The color space was measured.
The measurement results are shown in Table 1.

As shown in Table 1, various plant raw materials before the urethane bond formation reaction have a high degree of coloring. By reacting this raw material with a compound represented by any one of the general formulas (11) to (13), a powder (lignin) having a higher whiteness (L *) than the raw material could be recovered. Furthermore, the color space was different depending on the modifying group of the reactive compound.

<Test Example 2> Molecular structure of reaction product (1) FT-IR measurement
A sample obtained by modifying dodecylisocyanate with isolated lignin with reference to Green Chem., 2016, 18, 5962 and JP-A-2019-154381 (hereinafter referred to as "Dod-I modified isolated lignin"). Was prepared. Specifically, 500 g of vegetable powder obtained by crushing cedar into a size of about 0.02 to 5 mm with a cutter mill or a jet mill is immersed in 4.5 L of 100 mM phosphate buffer (pH = 5.0) overnight, and the wet crusher LMZ4 It was put into (trade name, manufactured by Ashizawa Finetech) together with a buffer solution. A cellulase / hemicellulase mixture (50 mL each for Optimash XL and Optimash BG) manufactured by DuPont Genecoa was further added, and wet pulverization was performed using 0.5 mm diameter beads made of zirconia metal while keeping the temperature at 50 ° C. When the average particle size reached 10 μm, the beads were replaced with 0.1 mm diameter beads made of zirconia metal. The wet pulverization was carried out for a total of 4 hours. Centrifugation (10,000 xg, 30 minutes) gave lignin as a residue. Using the obtained lignin and dodecyl isocyanate, a urethane bond forming reaction was carried out in the same manner as in Example 3 to prepare a powder (Dod-I modified isolated lignin).
The lignin powder prepared in Examples 2 and 4 and the Dod-I modified isolated lignin were subjected to FT-IR measurement in total reflection mode using an FT-IR apparatus (NICOLET6700) manufactured by Thermo Fisher.
The results are shown in FIG. As shown in FIG. 1, the NH expansion and contraction vibration peak and the peak group considered to be derived from the lignin aromatic ring were confirmed. The NH expansion and contraction vibration peak is derived from a urethane bond formed by a reaction between a hydroxyl group or an alcoholic hydroxyl group having a guaiacol structure and an isocyanate group. Furthermore, the peaks of the lignin powders prepared in Examples 1 and 2 coincided with the peaks of the existing Dod-I modified isolated lignin.
Therefore, from these results, it was confirmed that an addition reaction occurred between the lignin and the isocyanate group in all the reaction systems.

(2) Measurement of ultraviolet-visible absorption spectrum The white powder of lignin prepared in Example 1 was dissolved in ethanol, the obtained ethanol solution was injected into a quartz cell, and a spectrophotometer (U-2910, manufactured by Hitachi Koki) was used. Then, the ultraviolet-visible absorption spectrum was measured at room temperature.

The results are shown in FIG.
As shown in FIG. 2, peaks derived from absorption of lignin by guaiacyl (280 nm) and absorption by the syringyl skeleton (270 nm) were confirmed (see IAWA Bull. Ns 1992, 13 (1), 105).

From the FT-IR measurement results and the UV-visible absorption spectrum measurement results, the white solid prepared in Examples 1 and 2 was identified as a lignin composition.

<Test Example 3> Properties of reaction product The lignin powder prepared in Example 2 was dissolved and mixed in chloroform at a ratio of 5% by weight to polyepsylon caprolactam (PCL, manufactured by Sigma-Aldrich), and glass was used. The composite was prepared by casting and drying on a substrate. The weight loss due to heating was measured using a thermal weight measuring device (Thermo plus EVO2, manufactured by Rigaku Co., Ltd.) at a heating rate of 10 ° C. in an air atmosphere. The results are shown in FIG.
As shown in FIG. 3, the pyrolysis temperature increased in the composite of lignin powder and PCL. Specifically, the temperature at which the weight of the complex reaches half the weight reduction is about 60 ° C higher than that of PCL alone. Therefore, it is suggested that the lignin obtained by the present invention has a possibility of being used as a heat-resistant filler.

As described above, according to the present invention, colored lignin can be decolorized, and decolorized lignin can be produced. Further, since lignin is expected as a functional substance, the decolorized lignin obtained in the present invention can be applied to various uses.

Claims (6)

A method for decolorizing lignin, which comprises reacting a plant or a processed plant product containing 10 to 50% by mass of lignin with a compound represented by any one of the following general formulas (11) to (13).

RN = C = O General formula (11)
R-COOH general formula (12)
R-OH general formula (13)

(In the general formulas (11) to (13), R represents an alkyl group, an aralkyl group, an aryl group, an alkyl halide group, an aryl halide group, a sulfonyl group, or a silyl group.) A decolorized lignin obtained by reacting a plant or a processed plant product containing 10 to 50% by mass of lignin with a compound represented by any one of the following general formulas (11) to (13) to obtain bleached lignin. Preparation method.

RN = C = O General formula (11)
R-COOH general formula (12)
R-OH general formula (13)

(In the general formulas (11) to (13), R represents an alkyl group, an aralkyl group, an aryl group, an alkyl halide group, an aryl halide group, a sulfonyl group, or a silyl group.) The method according to claim 1 or 2, wherein the compound represented by any one of the general formulas (11) to (13) is an isocyanate compound represented by the following general formula (21).

R'-N = C = O General formula (21)

(In the general formula (21), R'represents an alkyl group, an aralkyl group, or an aryl group.) The method according to any one of claims 1 to 3, wherein the obtained decolorized lignin is in the form of powder. The plants are cedar ( Cryptomeria japonica ), beech ( Fagus crenata Blume), pine ( Pinus ) plant, balsa ( Ochroma lagopus ), parrot's feather ( Myriophyllum aquaticum ), moso bamboo ( Phyllostachys heterocycla ), rice ( Oryza sativa ). Triticum aestivum ), corn ( Zea mays subsp. Mays (L.) Iltis), Erianthus arundinaceus , Miscanthus sinensis , Saccharum officinarum , Phragmites australis , Giant Reed ( Arundo ) , Abra palm (oil palm, Elaeis ), Nypa fruticans Wurmb, Sato palm ( Arenga pinnata or Arenga saccharifera ), Hoteia oi ( Eichhornia crassipes ), Senninmo ( Potamogeton maackianus ), Parrot's feather ( Egeria ) ( Elodea nuttallii ), Akamoku ( Sargassum horneri ), Hondawara ( Sargassum fulvellum ), Aosa ( Ulva ), Ichiijita ( Caulerpa taxifolia ), Sea grapes ( Caulerpa lentillifera ), and at least one species of the genus Eucheuma. The method according to any one of claims 1 to 4, which is a plant of. The plant-treated product is chipper-treated, dry-grinding, wet-grinding, grinding, saccharification, fermentation, cooking, blasting, sub-critical water treatment, decomposition treatment with ionic liquid, acid treatment, base treatment and The method according to any one of claims 1 to 5, wherein at least one treatment selected from the group consisting of microwave treatment is performed.

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