JP2021155661A - Separation method of soda lignin - Google Patents

Abstract

To provide a method of efficiently separating soda lignin from a black liquor discharged from a step of steaming the conifer with soda.SOLUTION: A method formed by including: a step a) in which after acid and/or carbon dioxide are added to the black liquor to precipitate lignin under conditions of lower than pH 10 and at temperatures of 60 to 80°C, followed by dewatering; a step b) of adjusting to lower than pH 3 by suspending the lignin precipitate obtained in the step a) to precipitate the lignin; and a step c) of dewatering and cleaning the lignin precipitate obtained in the step b), in which the lignin is separated from the black liquor discharged from the step of steaming the conifer with soda.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for efficiently separating lignin dissolved from black liquor discharged from a step of evaporating softwood chips with soda.

In recent years, as a substitute for petroleum, it has been studied to use lignin as a raw material by converting it into a phenol resin, an epoxy resin or the like. Lignin is abundant in wood, but in order to extract it, mechanical treatment such as chemical treatment using acid, alkali or organic solvent, crushing, etc. is required. For example, in the sulfite cooking method, a mixed solution of acidic sulfite and sulfite is added and steamed at 130 to 145 ° C. to elute lignin in wood as lignin sulfonate (for example, Patent Document 1), and in the craft cooking method. , caustic soda (NaOH) and sodium sulfide _(Na 2 S) was added chemicals mainly, and cooked at about 150-170 ° C., eluting as kraft lignin. Apart from these steaming methods, it has been studied to add an alkaline aqueous solution such as caustic soda to elute lignin (Patent Document 2).

It is also important to efficiently separate the extracted lignin. For example, it is disclosed that a black liquor obtained by a craft cooking method or the like is acidified to precipitate lignin and dehydrated, and a lignin-filtered cake is washed to obtain lignin (Patent Document 3).

Japanese Unexamined Patent Publication No. 2001-89986 Japanese Unexamined Patent Publication No. 2014-208803 Japanese Patent Application Laid-Open No. 2008-513549

However, since the method of Patent Document 3 uses kraft black liquor as a raw material, it is inevitable that hydrogen sulfide having an odor and toxicity will be generated when the black liquor is adjusted to be acidic. In addition, since sodium sulfide is used in kraft cooking, there is a concern that sulfur components may remain in the final lignin product.

An object of the present invention is a method for efficiently separating lignin from the black liquor discharged from the step of steaming soda.

As a result of repeated studies to achieve these objectives, the present inventors added acid and / or carbon dioxide to the black liquor discharged from the step of soda-melting coniferous trees to have a pH of less than 10 and a temperature of 60 to 80. It has been found that the above object can be achieved by precipitating lignin under the condition of ° C. and further acidifying the pH.

That is, the present invention provides the following invention.
(1) A method for separating lignin from black liquor discharged from a step of evaporating coniferous trees with soda, which comprises the following steps.
a) A step of adding an acid and / or carbon dioxide to a black liquor to precipitate lignin under the conditions of a pH of less than 10 and a temperature of 60 to 80 ° C., and then dehydrating to obtain a lignin precipitate A.
b) A step of suspending the lignin precipitate A obtained in step a) and adjusting the pH to less than 3 to precipitate lignin.
c) A step of dehydrating and washing and dehydrating the lignin precipitate obtained in step b) to obtain a lignin precipitate C.
(2) The method according to (1), wherein the conifer is Sugi.
(3) The method according to any one of (1) and (2), wherein dehydration in the steps a) and / or step c) is performed by a filter press device.
(4) The method according to any one of (1) to (3), wherein in the step b), the lignin precipitate A is suspended and then an acid is added to bring the pH to less than 3.
(5) The method according to any one of (1) to (3), wherein the lignin precipitate A is suspended in an acidic solution to have a pH of less than 3 in the step b).
(6) The method according to any one of (1) to (5), wherein washing is performed until the electric conductivity of the washing filtrate obtained in the step c) becomes 0.2 S / m or less.
(7) The solid content of the black liquor is 10% by mass or more and 40% by mass or less, and the solid content of the lignin precipitate C is 25% or more according to any one of (1) to (6). Method.

According to the present invention, it is possible to efficiently separate lignin from the black liquor discharged from the step of steaming coniferous trees with soda.

The present invention is a method for separating lignin from the black liquor discharged from the step of soda-melting coniferous trees. Steps of precipitating and then dehydrating lignin, b) Suspending the lignin obtained in step a) and adjusting the pH to less than 3 to precipitate lignin, c) Dehydrating and washing dehydrating the lignin obtained in step b) It is a method including the step of performing. Hereinafter, each step of the present invention will be specifically described.

Conifers used as raw materials for soda cooking include sugi, spruce, karamatsu, black pine, todomatsu, himekomatsu, ichii, cat, picea torano, iramomi, inumaki, fir, sawara, togasawara, asunaro, hiba, tsuga, rice tsuga, hinoki, ichii Examples include spruce, yellow cedar (beihiba), lawson hinoki (beihi), douglas fir (bei pine), sitka spruce (bei touhi), radiata pine, eastern spruce, eastern white pine, western larch, western fur, western hemlock, tamarac, etc. NS. As the conifer to be used, Sugi is more preferable because it can be easily obtained in Japan.

The softwood chips (softwood chips) are put into a cooking pot together with a cooking liquid composed of a caustic soda solution and used for soda cooking. Further, there is no particular limitation on the cooking type such as 1 Vessel liquid phase type, 1 Vessel gas phase / liquid phase type, 2 Vessel liquid phase / gas phase type, and 2 Vessel liquid phase type. That is, the step of impregnating the alkaline aqueous solution of the present application and holding the alkaline aqueous solution may be installed separately from the device or site for the purpose of the conventional permeation treatment of the cooking liquid. Preferably, the unbleached pulp that has been digested is washed with a washing device such as a diffusion washer after extracting the cooking liquid.

Soda cooking can be performed by putting wood chips together with the cooking liquid in a pressure-resistant container, but the shape and size of the container are not particularly limited. The liquid ratio of the wood chip to the cooking liquid can be, for example, 1.0 to 40 L / kg, preferably 1.5 to 30 L / kg, and even more preferably 2.0 to 30 L / kg. In yet another embodiment, the liquid ratio of the wood chip to the chemical solution can be, for example, 1.0 to 5.0 L / kg, preferably 1.5 to 4.5 L / kg, and 2.0 to 4. 0 L / kg is more preferable.

Further, in the soda cooking of the present invention, various cooking aids can be used in combination in addition to caustic soda (NaOH). For example, an alkaline cooking liquid containing 0.01 to 5% by mass of a quinone compound per absolute dry tip may be added to the cooking pot. If the amount of the quinone compound added is less than 0.01% by mass, the amount of lignin extracted into the black liquor is not sufficient. Further, even if the addition amount of the quinone compound exceeds 5% by mass, no further improvement in the extraction amount of lignin is observed.

The quinone compound used is a quinone compound as a so-called known cooking aid, a hydroquinone compound or a precursor thereof, and at least one compound selected from these can be used. Examples of these compounds include anthraquinone, dihydroanthraquinone (eg, 1,4-dihydroanthraquinone), tetrahydroanthraquinone (eg, 1,4,4a, 9a-tetrahydroanthraquinone, 1,2,3,4-tetrahydroanthraquinone). , Methylanthraquinone (eg 1-methylanthraquinone, 2-methylanthraquinone), methyldihydroanthraquinone (eg 2-methyl-1,4-dihydroanthraquinone), methyltetrahydroanthraquinone (eg 1-methyl-1,4,4a) , 9a-tetrahydroanthraquinone, 2-methyl-1,4,4a, 9a-tetrahydroanthraquinone) and other quinone compounds such as anthraquinone (generally 9,10-dihydroxyanthraquinone) and methylanthrahydroquinone (eg, 2-methyl). Anthraquinone), dihydroanthraquinone (eg, 1,4-dihydro-9,10-dihydroxyanthraquinone) or an alkali metal salt thereof (eg, disodium salt of anthraquinone, 1,4-dihydro-9,10-) It is a hydroquinone compound such as a disodium salt of dihydroxyanthraquinone), and examples thereof include precursors such as anthraquinone, anthraquinone, methylanthronone, and methylanthraquinone. These precursors have the potential to be converted to quinone or hydroquinone compounds under cooking conditions.

The cooking liquid can have a caustic soda addition rate of 1 to 50% by mass per mass of dry wood chips, preferably 10 to 30% by mass. If the addition rate is less than 1% by mass, the removal of lignin and hemilulose is insufficient, and if it exceeds 50% by mass, the yield and quality are lowered. The soda cooking is preferably carried out in a temperature range of 120 to 180 ° C, more preferably 140 to 160 ° C. If the temperature is too low, delignin (decrease in copper value) is insufficient, while if the temperature is too high, the degree of polymerization (viscosity) of cellulose decreases. The cooking time in the present invention is the time from when the cooking temperature reaches the maximum temperature until the temperature starts to decrease. The cooking time is preferably 60 minutes or more and 600 minutes or less, and 120 minutes or more and 360 minutes or less. Is even more preferable. If the cooking time is less than 60 minutes, pulping does not proceed, and if it exceeds 600 minutes, the pulp production efficiency deteriorates, which is not preferable.

Further, in the soda cooking in the present invention, the treatment temperature and the treatment time can be set by using the H factor (Hf) as an index. The H factor is a guideline for expressing the total amount of heat given to the reaction system in the cooking process, and is expressed by the following formula. The H factor is calculated by integrating the time from the time when the chips and water are mixed to the time when the cooking is completed. The H factor is preferably 250 to 6000.

Hf = ∫exp (43.20-16113 / T) dt
In the present invention, the unbleached (unbleached) pulp obtained after cooking can be subjected to various treatments, if necessary. For example, the unbleached pulp obtained after soda cooking can be bleached.

<Step a): A step of adding an acid and / or carbon dioxide to a black liquor to precipitate lignin under the conditions of a pH of less than 10 and a temperature of 60 ° C. to 80 ° C., and then dehydrating to obtain a lignin precipitate A>.
Acid and / or carbon dioxide are added to the black liquor obtained after soda cooking to make a suspension with a pH of less than 10 so that the lignin dissolved in the black liquor is precipitated as an insoluble matter. It becomes possible. This step may be repeated twice or more. The pH of the black liquor may be 1-9 or may be adjusted to 2-8. When the pH of the black liquor is 10 or more, insoluble matter of lignin is not sufficiently produced. The acid used may be an inorganic acid or an organic acid. Examples of the inorganic acid include sulfuric acid, sulfurous acid, hydrochloric acid, nitric acid, nitrite, phosphoric acid, carbon dioxide and the like, and sulfuric acid is preferable. Further, the residual acid discharged from the chlorine dioxide generator may be used. Examples of the organic acid include acetic acid, lactic acid, oxalic acid, citric acid, formic acid and the like. The black liquor can be concentrated using an evaporator or the like before adjusting the pH, and the solid content is preferably 10% by mass or more and 40% by mass or less, preferably 18% by mass or more and 30% by mass or less. More preferably. If the solid content is too low, the precipitation of lignin is insufficient, and the efficiency of lignin recovery is also poor. Further, if the solid content is too high, the viscosity of the black liquor becomes high, and it becomes difficult to recover the precipitate of lignin.

The temperature at which the pH of the black liquor is adjusted to less than 10 is preferably room temperature to 100 ° C. When the temperature exceeds 100 ° C., lignin is condensed, which makes it difficult to separate lignin.

When acid and carbon dioxide are added in the above-mentioned step of adjusting the pH to less than 10, the treatment temperature is preferably about 60 to 80 ° C. Below 60 ° C, sufficient aggregation of lignin does not occur and separation becomes difficult. Further, in the range exceeding 80 ° C., the lignin aggregates soften, which makes it difficult to collect them by a filter press. The method of adding carbon dioxide is not particularly limited, but there are a method of blowing under atmospheric pressure and a method of blowing carbon dioxide in a closed container and pressurizing (0.1 to 1 MPa). The carbon dioxide may be pure carbon dioxide gas, but gas containing carbon dioxide generated from combustion exhaust gas discharged from an incinerator, a boiler or the like, a lime firing step or the like can also be used.

If necessary, a flocculant may be added to promote the precipitation of lignin. Examples of the flocculant include aluminum sulfate band, aluminum chloride, polyaluminum chloride, polyamine, DADMAC, melamine colloid, gin andiazide and the like.

By adding acid and / or carbon dioxide to the black liquor to adjust the pH of the black liquor to less than 10, a cake-like precipitate containing lignin is obtained. The precipitate is separated by dehydration and washing with water. As an apparatus for dehydrating and washing the precipitate, a filter press, a drum press, a centrifugal dehydrator, a suction filtration apparatus and the like can be used. The water used for washing is not particularly limited, but industrial water, tap water, etc. can be used, the pH is 1 to 9, the temperature is 20 to 80 ° C, and the electrical conductivity is 0.2 S / m or less. It is preferable to have.

<Step b): A step of suspending the lignin precipitate obtained in step a) and adjusting the pH to less than 3 to precipitate the lignin.
In step b), water is added to the cake-like lignin precipitate A obtained in step a) to suspend it. The water used at this time may be the same water as the water used for washing in step a). Next, an acid is added to the lignin suspension to adjust the pH to less than 3, and the lignin is precipitated. The acid used may be either an inorganic acid or an organic acid used in step a). Examples of the inorganic acid include sulfuric acid, sulfurous acid, hydrochloric acid, nitric acid, nitrite, phosphoric acid, carbon dioxide and the like, and sulfuric acid is preferable. Further, the residual acid discharged from the chlorine dioxide generator may be used. Examples of the organic acid include acetic acid, lactic acid, oxalic acid, citric acid, formic acid and the like. Further, the lignin precipitate A may be suspended in an acidic solution prepared by adding an acid in advance. The acid used to prepare the acidic solution may be either an inorganic acid or an organic acid used in step a). Examples of the inorganic acid include sulfuric acid, sulfurous acid, hydrochloric acid, nitric acid, nitrite, phosphoric acid, carbon dioxide and the like, and sulfuric acid is preferable. Further, the residual acid discharged from the chlorine dioxide generator may be used. Examples of the organic acid include acetic acid, lactic acid, oxalic acid, citric acid, formic acid and the like.

<Step c): Step of dehydrating and washing the lignin precipitate obtained in step b)>
Step c) is a step of dehydrating and washing the cake-like lignin precipitate obtained in step b). It is necessary to sufficiently reduce the impurity content of the finally obtained lignin, and it is desirable to carry out the washing until the electrical conductivity of the washing filtrate becomes 0.2 S / m or less. Under conditions where the electrical conductivity of the wash filtrate exceeds 0.2 S / m, inorganic salts such as sodium may remain in the final lignin, which is not desirable. As an apparatus for dehydrating and washing the lignin precipitate, a filter press, a drum press, a centrifugal dehydrator, a suction filtration apparatus and the like can be used as in step a). The water used for washing the precipitated lignin may be the same water as the water used for washing in step a) or step c). The solid content of the precipitate C is preferably 25% or more. If the concentration of solids is low, the handling of the prepared lignin will be poor. In addition, it takes a long time to remove water when the product is dried.

Lignin can also be purified by adding an organic solvent to the lignin precipitate C obtained in step c) to dissolve it and separating the insoluble matter which is an impurity. The organic solvent to be added is a non-solvent or a poor solvent for saccharides, for example, alcohols containing methanol, ethanol, isopropyl alcohol, 2-methoxyl ethanol, butanol and the like, ethers including 1,4-dioxane, tetrahydrofuran and the like. , Ketones including acetone and methyl ethyl ketone, nitriles including acetonitrile, amines including pyridine, amides including formamide, esters containing ethyl acetate, methyl acetate, etc., aliphatic hydrocarbons including hexane, etc. , Aromatic hydrocarbons containing benzene, toluene and the like, one or more of them may be mixed, or one or more of them may be mixed and water may be added. Acetone is particularly preferable. As a method for solid-liquid separation of the insoluble matter in the suspension, a filter press, a drum press, a centrifugal dehydrator, a suction filtration device, or the like can be used.

The lignin obtained in the present invention can be used as a thermosetting resin, a dispersant, and an adhesive. Further, by further reducing the molecular weight, it can be used as a phenol resin raw material or an epoxy resin raw material.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto. In this specification,% indicates mass% unless otherwise specified.
<Soda cooking>
25 kg of sodium hydroxide and 20 g of anthraquinone were added to a rotary reaction kettle containing 100 kg (absolutely dry) of cedar chips. Next, steam was blown in while rotating, the temperature was raised to 160 ° C., and the reaction was carried out for 4 hours. After the reaction, it was separated by filtration to obtain a black liquor.
[Example 1]
<Step a)>
160 L of black liquor (solid content concentration 19.3%) obtained from soda cooking was charged into a reaction vessel having a capacity of 300 L and heated to 80 ° C. Carbon dioxide was then introduced into the reaction vessel at a rate of 0.03 kg per minute until the pH reached 8.0. The precipitated lignin was subjected to a filter press (Lab Pressure Filter VPA 04, manufactured by Metso) for dehydration. As the filter cloth, polypropylene plain weave P28 (manufactured by Yabuta Sangyo, air permeability 1.0 cm ³ / cm ² / sec) was used. The obtained lignin weighed 27.9 kg (9.8 kg in terms of dryness).
<Step b)>
35.9 kg of water was added to 26.7 kg (dry equivalent 9.4 kg) of the cake-like lignin precipitate obtained in step a), and the mixture was suspended in a reaction vessel while adjusting to 50 ° C., followed by 8N sulfuric acid (Takasugi Pharmaceutical Co., Ltd.) was added at an addition rate of 0.1 kg / min using a liquid feed pump. At this time, while monitoring the pH of the suspension, the addition of sulfuric acid was stopped when the pH reached 2.0. The amount of sulfuric acid added was 6.1 kg. Then, stirring was continued for 1 hour to precipitate lignin.
<Step c)>
The cake-like lignin precipitated in step b) was subjected to a filter press in the same manner as in step a) to dehydrate. As the filter cloth, polypropylene plain weave P28 (manufactured by Yabuta Sangyo, air permeability 1.0 cm ³ / cm ² / sec) was used. Next, washing was carried out by passing industrial water (pH 7.2) while retaining the dehydrated cake-like lignin in the filter press. The end point of the washing was a point where the electrical conductivity of the washing filtrate was 0.2 S / m or less. The results of plotting the electrical conductivity and pH of the wash filtrate against the wash ratio are shown in FIG. The electrical conductivity and pH were measured with a portable pH / ORP / electrical conductivity meter D-74 (manufactured by HORIBA).

Next, the filter chamber of the filter press was pressed to 7.5 bar and squeezed, and then air was introduced into the filter chamber to remove as much water as possible from the lignin to obtain 17.5 kg of lignin (6.3 kg in terms of dryness). rice field. The obtained lignin was subjected to a fluorescent X-ray analyzer EDX-8000 (manufactured by Shimadzu Corporation) to quantify the Na concentration. As a result, the Na content was below the detection limit. From this, it can be seen that the degree of lignin cleaning can be evaluated by measuring the electrical conductivity of the cleaning filtrate.
[Example 2]
The introduction of carbon dioxide gas in <Step a)> of Example 1 was carried out in the same manner except that the temperature condition was changed by 60 ° C., and the mixture was subjected to a filter press.
[Comparative Example 1]
The introduction of carbon dioxide gas in <Step a)> of Example 1 was carried out in the same manner except that the temperature condition was changed by 50 ° C., and the mixture was subjected to a filter press.
[Comparative Example 2]
The introduction of carbon dioxide gas in <Step a)> of Example 1 was carried out in the same manner except that the temperature condition was changed by 90 ° C., and the mixture was subjected to a filter press.
As shown in the table below, when the temperature was low, the aggregation of lignin was weak and it was difficult to recover it with a filter press. In addition, when the temperature was high, lignin had a sticky property and was difficult to recover by a filter press.

The graph of FIG. 1 is a result of plotting the electrical conductivity of the washing filtrate against the washing ratio when the cake-shaped lignin was washed in step c) of the example. The cleaning ratio is V / V0 when the amount of water contained in the cake-like lignin in the filter chamber of the filter press is V0 and the amount of the cleaning filtrate discharged by cleaning is V. When V / V0 is 1, it indicates that the water contained in the cake-like lignin has been replaced by an equal amount.

Claims (7)

A method for separating lignin from black liquor discharged from a step of evaporating coniferous trees with soda, which comprises the following steps.
Step a) A step of adding an acid and / or carbon dioxide to a black liquor to precipitate lignin under the conditions of a pH of less than 10 and a temperature of 60 ° C to 80 ° C, and then dehydrating to obtain a lignin precipitate A.
Step b) A step of suspending the lignin precipitate A obtained in step a) and adjusting the pH to less than 3 to precipitate lignin.
Step c) A step of dehydrating and washing and dehydrating the lignin precipitated in step b) to obtain a lignin precipitate C. The method according to claim 1, wherein the conifer is Sugi (Cryptomeria japonica). The method according to claim 1 or 2, wherein dehydration in the steps a) and / or step c) is performed by a filter press device. The method according to any one of claims 1 to 3, wherein in the step b), the lignin precipitate A is suspended and then an acid is added to bring the pH to less than 3. The method according to any one of claims 1 to 3, wherein the lignin precipitate A is suspended in an acidic solution to have a pH of less than 3 in the step b). The method according to any one of claims 1 to 5, wherein the washing and dehydration is performed until the electric conductivity of the washing filtrate obtained by the washing and dehydrating in the step c) becomes 0.2 S / m or less. The method according to any one of claims 1 to 6, wherein the solid content of the black liquor is 10% by mass or more and 40% by mass or less, and the solid content of the lignin precipitate C is 25% or more.

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