CN102391522A - Preparation method of novel water-soluble ligin - Google Patents

Abstract

The invention discloses a preparation method of a novel water-soluble lignin. The preparation method is as follows: after simple pretreatment of the herbal plant fiber raw material, cooking is carried out by using a solid alkali active oxygen cooking process, the solution after cooking is sieved and separated to obtain yellow liquid, and the yellow liquid is centrifuged or left standing to remove sediment to obtain yellow liquid Clear liquid, the clear liquid of yellow liquid is evaporated and concentrated or a small amount of inorganic acid is added dropwise to separate lignin products. The solid alkali used in this method is a loaded solid alkali, which is resistant to water erosion, contains one or more of metal ions such as Ca, Mg, Al, Zn, etc., and can be easily processed and reused. The active oxygen used is H ₂ O ₂ and A combination _{of O2} , or a combination of _H2O2 and _O3 . The pH of the yellow liquid obtained by this method is between 7.3 and 7.8, which is close to neutral, so the obtained lignin is also different from alkali lignin; the lignin obtained by this method does not introduce other groups (such as sulfur groups), and the lignin High purity, so it has a wide range of application prospects.

Description

A kind of preparation method of novel water-soluble lignin

technical field

The invention relates to a preparation method of lignin, in particular to a preparation method of novel water-soluble lignin.

Background technique

Lignin is a kind of high polymer ubiquitous in plants, and it forms the skeleton of plants together with cellulose and hemicellulose. At present, commercial lignin is generally separated from plant raw materials by chemical pulping, and then extracted from papermaking waste liquor. Commercial lignin is mainly based on alkali lignin and lignosulfonate. Alkali lignin is mainly derived from alkaline pulping black liquor such as sulfate method, caustic soda method, caustic soda-AQ method, etc. Alkali lignin is soluble in alkaline medium and has high reactivity. Lignosulfonate is produced by sulfite pulping. Lignosulfonate is the most used type of commercial lignin, which has good water solubility and wide application. There are two main ways to apply lignin: 1. Use methods such as acid precipitation, solvent extraction or ultrafiltration to separate lignin from black liquor and then use it; direct use. At present, lignin has been widely used in polymer materials, petrochemicals, dyes, leather, construction industry, agriculture and animal husbandry, and water treatment industries, so lignin is a very promising natural polymer material.

Due to the preparation process and other reasons, the purity of most commercial lignin is low, and the preparation process has a certain impact on the environment. For example, in the sulfite cooking process, a large amount of sulfur-containing compounds are used, which will produce malodorous gases and seriously pollute the environment. During the alkaline pulping process, the pH of the black liquor is generally above 11-12, the consumption of chemicals is large, and some groups, such as sulfonic acid groups, are introduced into the lignin, and the lignin structure is also severely damaged. It will limit the application of lignin in some industries.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art and provide a novel method for preparing water-soluble lignin. The solid color of the lignin is light yellow powder, very soluble in water, its aqueous solution is transparent light yellow, has the aroma of wood, the lignin does not contain sulfur groups, and has few impurities;

The purpose of the present invention is also to provide an environment-friendly preparation method suitable for both laboratory preparation and large-scale industrial production of novel lignin.

A kind of preparation method of novel water-soluble lignin, comprises the steps:

(1) Crush the herbaceous plant fiber raw material into strips with a length of 3-7 cm;

(2) Mix the raw materials, solid alkali, active oxygen, and water in the reactor in step (1), and cook the mixed solution in the reactor at 120-180°C and 1-3 MPa for 1 -3 hours;

(3) Sieving and separating the cooked solution to obtain yellow liquid and solid residue;

(4) Centrifuge or statically settle the yellow liquid to obtain the clear liquid of the yellow liquid and the residue containing solid alkali;

(5) After adding mineral acid to the yellow liquid clear liquid, a slightly yellow precipitate, namely lignin, is precipitated.

The volume ratio of the inorganic acid added in the step (5) is 0.5-3%.

The inorganic acid is more than one of sulfuric acid, hydrochloric acid, phosphoric acid or nitric acid.

The ratio of water and raw materials added in the step (2) is 4-10, the amount of solid alkali is 5-30% relative to the absolute dry raw material, and the amount of active oxygen is 2-15% relative to the absolute dry raw material.

The solid base in the step (2) is a water-resistant loading type solid base, and the solid base contains MgO, CaO, Al ₂ O ₃ , ZnO, Mg(OH) ₂ , Ca(OH) ₂ , Al(OH) ₃ or more than one of Zn(OH) ₂ ; the carrier is NaX or MgX, and the active oxygen is a combination of H ₂ O ₂ and O ₂ , or a combination of H ₂ O ₂ and O ₃ .

The yellow liquid serum obtained in the step (4) is dried to obtain lignin containing carbohydrates.

The plant fiber raw material is more than one of wheat straw, rice straw, bagasse or corn stalks.

When plant raw materials with high silicon content are used, the raw materials need to be washed.

Burn the residue containing solid base at 350-750°C for 1-3 h to obtain solid base again.

The lignin obtained by the solid alkali active oxygen cooking process adopted in the present invention has the following advantages: 1. Only solid alkali and active oxygen are added in the cooking process, and no sulfide is contained, so the cooking process will not produce malodorous gas, and the solid alkali It can be reused, which is an environmentally friendly process; 2. Among the active oxygen used in this method, except for H ₂ O ₂ , the consumption of O ₂ or O ₃ is only 15-20%, and the remaining active oxygen can be recycled for continued use ; 3. The concentration of yellow liquid obtained by this method is higher, which is beneficial to the evaporation and concentration extraction of lignin. When using the acid analysis method, the lignin yield is also higher than that of traditional alkali lignin; 4. Only a small amount of yellow liquid exists in the cooking process. Metal ions and carbohydrates, less impurities, higher lignin purity; 5. Lignin only reacts with active oxygen during cooking, no other groups are introduced, lignin properties change less, and its practicability is stronger; 6. In terms of cost, the cost of solid alkali active oxygen cooking is equivalent to or even lower than that of traditional technology, which is mainly due to the fact that solid alkali can be reused.

Compared with traditional lignosulfonate, the present invention has the following advantages: 1. Only a small amount of metal ions and part of hemicellulose exist in the yellow liquid obtained by the process, with less impurities and higher lignin purity; 2. When cooking Lignin only reacts with active oxygen and does not introduce other groups. The change of lignin is relatively small, mainly due to the oxidation and breakage of lignin side chains. There are more active groups in lignin, and its practicability is stronger; 3. This lignin is different from traditional alkali lignin, it can be completely dissolved under neutral or slightly acidic conditions, and it is a new type of lignin.

Detailed ways

The present invention will be further described below in conjunction with the examples. It should be noted that the examples are not intended to limit the protection scope of the present invention. In order to avoid the influence of various errors during the experiment, the following examples mainly carry out statistical calculations for the cooked yellow liquid.

Example 1

The plant fiber raw material is bagasse, by weight, the cellulose content is 36.8%, the hemicellulose content is 30.2%, the lignin content is 25.6%, and the raw material length is 3-5 cm. The type of solid base used is MgO, and the carrier is NaX. In terms of weight, the amount of solid base is equivalent to 25% of the absolute dry raw material. The active oxygen used is O ₂ and H ₂ O ₂ , the oxygen pressure is 1.2 MPa, the amount of H ₂ O ₂ is 2% (for absolute dry raw materials), and the solid-liquid ratio is 6. The reaction temperature is 150°C, and the reaction time includes: the heating time is about 2 h (from room temperature to 150°C), and the holding time is 1.2 h (the temperature is kept at 150°C). After the reaction is finished, the raw material residue and the yellow liquid are separated by sieving, and the yellow liquid is centrifuged or left to settle to obtain a precipitate and a clear liquid of the yellow liquid. The resulting precipitate (containing a small amount of lignin) was calcined in a muffle furnace at 575°C for 2 h to obtain a solid base again, and the recovery rate of the solid base was calculated to be 56.2%. The lignin concentration in the gained yellow liquid clear liquid is 3.9%, and solid content is 8.1%, adds the concentrated sulfuric acid of 2% volume in the yellow liquid clear liquid, can find that a large amount of yellowish precipitates are separated out in the yellow liquid clear liquid, and this precipitation is The lignin product can be separated from the yellow liquid clear liquid by centrifugation or static sedimentation, and the calculated yield of the lignin product is 32.2% (for the total amount of lignin in the yellow liquid, the same below), when the amount of sulfuric acid added is At 4%, 45.2% lignin can be obtained. If the amount of sulfuric acid continues to increase, the lignin yield will increase. When 4% volume of concentrated hydrochloric acid was added, the yield of lignin was 33.6%. It is also possible to directly evaporate and concentrate the yellow liquid to obtain a lignin product containing some carbohydrates. The yield of the crude lignin product is 45.8% (for absolute dry raw materials), and the lignin content in the crude lignin product is 50%. Above, has strong water absorption.

Example 2

The plant fiber is used as raw material of corn stalks. By weight, the cellulose content is 39.1%, the hemicellulose content is 24.0%, and the lignin content is 21.8%. The length of the raw material is 3-7 cm. The raw material is washed and air-dried before cooking. The type of solid base used is Al ₂ O ₃ , the carrier used is MgX, and the amount of solid base added is 8% of the dry raw material mass by weight. The active oxygen used is O ₂ and H ₂ O ₂ , the pressure of O ₂ is 1.8 MPa, the amount of H ₂ O ₂ is 5%, and the solid-liquid ratio is 10. The reaction temperature is 180°C, and the reaction time includes: the heating time is about 2.5 h, and the holding time is 2 h. After the reaction is finished, the raw material residue and the yellow liquid are separated by sieving, and the yellow liquid is centrifuged or left to settle to obtain a precipitate and a clear liquid of the yellow liquid. The obtained precipitate was calcined in a muffle furnace at 575°C for 2 h to obtain a solid base again, and the recovery rate of the solid base was calculated to be 36.2%. The lignin concentration in the obtained yellow liquid clear liquid is 1.8%, and the solid content is 4.6%. Add 2% volume of concentrated sulfuric acid in the yellow liquid clear liquid, and a large amount of slightly yellow lignin products are separated out in the yellow liquid clear liquid, which are separated by centrifugation. Or stand and settle to separate the lignin product, and the yield of the lignin product is 35.2% (to the total amount of lignin in the yellow liquor). Directly evaporating and concentrating the yellow liquid clear liquid, the crude lignin product yield is 43.9% (for absolute dry raw materials).

Example 3

The plant fiber raw material is wheat straw, by weight, the cellulose content is 38.3%, the hemicellulose content is 33.5%, and the lignin content is 16.9%. The length of the raw material is 3-7 cm. The raw material is washed and air-dried before cooking. The types of solid base used are MgO and CaO, the carrier used is NaX, and the amount of solid base added is 20% of the mass of the dry raw material. The active oxygen used is O ₃ and H ₂ O ₂ , the pressure of O ₃ is 1.0 MPa, the dosage of H ₂ O ₂ is 2%, and the solid-liquid ratio is 8. The reaction temperature is 150°C, and the reaction time includes: heating time of about 2.0 h, holding time of 3 h. After the reaction is finished, the raw material residue and the yellow liquid are separated by sieving, and the yellow liquid is centrifuged or left to settle to obtain a precipitate and a clear liquid of the yellow liquid. The yellow liquid was centrifuged or left to settle, and the resulting precipitate was calcined in a muffle furnace at 575°C for 2 h to obtain a solid base again. The recovery rate of the solid base was calculated to be 51.7%. The lignin concentration in the obtained yellow liquid clear liquid is 1.7%, and the solid content is 5.1%. Add 2% volume of concentrated sulfuric acid in the yellow liquid, and a large amount of yellowish lignin products are separated out in the yellow liquid clear liquid. The lignin product is separated by settling, and the yield of the lignin product is 34.0% (the total amount of lignin in the yellow liquid). Directly evaporating and concentrating the yellow liquid, the crude lignin product yield is 45.3% (for absolute dry raw materials).

Example 4

The plant fiber raw material is bagasse, by weight, the cellulose content is 36.8%, the hemicellulose content is 30.2%, the lignin content is 25.6%, and the raw material length is 3-5 cm. The type of solid base used is MgOH, the carrier used is MgX, and the amount of solid base added is 5% of the mass of the dry raw material. The active oxygen used is O ₂ and H ₂ O ₂ , the pressure of O ₂ is 2.5 MPa, the amount of H ₂ O ₂ is 5%, and the solid-liquid ratio is 8. The reaction temperature was 175°C, and the reaction time included: heating time of about 2.0 h, holding time of 2 h. After the reaction is finished, the raw material residue and the yellow liquid are separated by sieving, and the yellow liquid is centrifuged or left to settle to obtain a precipitate and a clear liquid of the yellow liquid. The resulting precipitate was calcined in a muffle furnace at 575°C for 2 h to obtain a solid base again, and the recovery rate of the solid base was calculated to be 30.2%. The lignin concentration in the obtained yellow liquid clear liquid is 3.0%, and the solid content is 5.8%. Add 2% volume of concentrated sulfuric acid in the yellow liquid, and a large amount of yellowish lignin products are separated out in the yellow liquid clear liquid. The lignin product is separated by settling, and the yield of the lignin product is 33.5% (the total amount of lignin in the yellow liquid). Directly evaporating and concentrating the yellow liquid clear liquid, the crude lignin product yield is 46.7% (for absolute dry raw materials).

Claims (9)

1. the preparation method of a new type water-solubility lignin is characterized in that comprising the steps:

(1) the herbage fibrous material is ground into strip, length is 3 ~ 7 cm;

(2) raw material, solid alkali, active oxygen, water after handling in the step (1) are placed in the reactor drum mix, the boiling 1-3 h under 120-180 ℃, the condition of 1-3 MPa of the mixing solutions in the reactor drum;

(3) solution after the boiling is carried out sieving separating, obtain yellow liquor and solid residue;

(4) centrifugal or quiescent settling obtains the yellow liquor clear liquid, contains the residue of solid alkali with yellow liquor;

(5) add mineral acid in the yellow liquor clear liquid after, separating out little yellow mercury oxide is lignin.

2. the preparation method of a kind of new type water-solubility lignin according to claim 1 is characterized in that the mineral acid volume ratio that said step (5) adds is 0.5-3 %.

3. the preparation method of a kind of new type water-solubility lignin according to claim 1 is characterized in that said mineral acid is more than one in sulfuric acid, hydrochloric acid, phosphoric acid or the nitric acid.

4. the preparation method of a kind of new type water-solubility lignin according to claim 1; It is characterized in that water and the add-on ratio of raw material: 4-10 in the said step (2); The solid alkali consumption is 5-30 % with respect to the over dry raw material, and the consumption of active oxygen is 2-15 % with respect to the over dry raw material.

5. the preparation method of a kind of new type water-solubility lignin according to claim 1 is characterized in that the solid alkali in the said step (2) is water-fast load-type solid, and said solid alkali contains MgO, CaO, Al ₂O ₃, ZnO, Mg (OH) ₂, Ca (OH) ₂, Al (OH) ₃Or Zn (OH) ₂In more than one, said carrier is NaX or MgX; Active oxygen is H ₂O ₂And O ₂Combination, or H ₂O ₂And O ₃Combination.

6. the preparation method of a kind of new type water-solubility lignin according to claim 1 is characterized in that the yellow liquor clear liquid that obtains in the said step (4) is dry, obtains containing the lignin of glucide.

7. the preparation method of the described a kind of new type water-solubility lignin of claim 1 is characterized in that said herbage fibrous material is more than one in wheat straw, straw, bagasse or the corn straw.

8. the preparation method of a kind of new type water-solubility lignin according to claim 7 is characterized in that needing when the silicone content of said herbage fibrous material is high carry out carrying out washing treatment to raw material.

9. the preparation method of a kind of new type water-solubility lignin according to claim 1 is characterized in that the residue that contains solid alkali obtaining solid alkali at 350-750 ℃ of following calcination 1-3 h.