Method for purifying lignin

Abstract

The present document discloses a method for purifying lignin. The method comprises steps of solvent dissolution, ultrasonic vibration, centrifugal filtration, stirring in water at a constant temperature, and membrane filtration and drying. In the present application, lignin extracted from a plant fiber raw material using an organic solvent is added to a specific solvent, and is purified by sequentially performing the steps of ultrasonic vibration, centrifugal filtration, stirring in water at a constant temperature, and membrane filtration and drying. Any of the steps cannot be omitted and the sequence thereof cannot be reversed. The steps are efficiently coordinated to achieve a synergistic effect, so as to remove impurities in lignin, and significantly improve the purity of the lignin while maintaining a high purification yield. The invention has broad application prospects and high market value.

Claims

1. A method for purifying lignin, comprising: (1) adding a crude acetone lignin to a purification solvent and performing ultrasonic vibration to obtain a primary product; (2) centrifuging the primary product to obtain a supernatant and a solid precipitate, washing and filtering the solid precipitate with the purification solvent, and mixing a filtrate with the supernatant to obtain a secondary product; (3) stirring the secondary product in a thermostated water bath to obtain a tertiary product; (4) adding distilled water to the tertiary product, stirring, and filtering through a filter membrane to obtain a cut-off precipitate; and (5) washing and drying the cut-off precipitate to obtain a purified acetone lignin; wherein the purification solvent is an ether, and the ether comprises diethyl ether; and wherein in step (1) the acetone lignin is purified using diethyl ether.

2. The method according to claim 1, wherein the crude acetone lignin is extracted from a plant fiber raw material.

3. The method according to claim 1, wherein a mass concentration of the purification solvent is 30%-100%.

4. The method according to claim 1, wherein a mass concentration of the primary product is 0.1%-90%.

5. The method according to claim 1, wherein a temperature for the ultrasonic vibration in step (1) is 20-80° C.

6. The method according to claim 1, wherein a rotation speed for the centrifuging in step (2) is 6,000-20,000 r/min.

7. The method according to claim 1, wherein a temperature of the thermostated water bath in step (3) is 20-80° C.

8. The method according to claim 1, wherein a solid-liquid ratio of the tertiary product to the distilled water is 1:(1-10).

9. The method according to claim 1, wherein a molecular weight cut-off of the filter membrane in step (4) is over 1,000.

10. The method according to claim 1, specifically comprising: (1) adding crude lignin to a purification solvent comprising diethyl ether with a mass concentration of 30%-100% and preforming ultrasonic vibration at 20-80° C. for 10-200 min to obtain a primary product with a concentration of 0.1-90%; wherein the crude lignin is a lignin extracted from a plant fiber raw material; (2) centrifuging the primary product at a rotation speed of 6,000-20,000 r/min to obtain a supernatant and a solid precipitate, washing and filtering the solid precipitate with the purification solvent, and mixing a filtrate with the supernatant to obtain a secondary product; (3) stirring the secondary product in thermostated water bath with a temperature of 20-80° C. at a shear velocity of 10-1,000 s.sup.−1 for 10-300 min to obtain a tertiary product; (4) adding distilled water to the tertiary product with a solid-liquid ratio of 1:(1-10), stirring for 1-10 min, and filtering through a filter membrane with a molecular weight cut-off of over 1,000 to obtain a cut-off precipitate; and (5) washing and drying the cut-off precipitate to obtain a purified lignin.

11. Lignin, wherein the lignin is obtained from purification by the method according to claim 1.

Description

DETAILED DESCRIPTION

(1) To further elaborate on the technical means adopted and the effects achieved in the present application, the solutions of the present application are further described below through specific examples, but the present application is not limited to the scope of the examples.

Example 1

(2) (1) Crude lignin that has been extracted using acetic acid was added to acetic acid with a mass concentration of 60% to prepare a solution, and ultrasonic vibration was performed at 60° C. for 100 min to obtain a primary product with a lignin mass concentration of 80%.

(3) (2) The primary product was centrifuged at a rotation speed of 10,000 r/min to obtain a supernatant and a solid precipitate, the solid precipitate was washed and filtered with acetic acid with a mass concentration of 60%, and the resultant filtrate was mixed with the supernatant to obtain a secondary product.

(4) (3) The secondary product was stirred in thermostated water bath with a temperature of 60° C. at a shear velocity of 800 s.sup.−1 for 150 min to obtain a tertiary product.

(5) (4) Distilled water was added to the tertiary product with a solid-liquid ratio of 1:5 and stirred for 5 min to precipitate lignin, and the mixed solution containing the precipitate was fed to a filter membrane device and filtered through a filter membrane with molecular weight cut-off of 2,000 to obtain a cut-off precipitate.

(6) (5) The cut-off precipitate was washed and then dried in a vacuum oven to obtain a lignin product with the solid content of over 85%.

Example 2

(7) (1) Crude ethanol lignin was added to methanol with a mass concentration of 90%, and ultrasonic vibration was performed at 20° C. for 200 min to obtain a primary product with a lignin mass concentration of 60%.

(8) (2) The primary product was centrifuged at a rotation speed of 8,000 r/min to obtain a supernatant and a solid precipitate, the solid precipitate was washed and filtered with methanol with a mass concentration of 90%, and the resultant filtrate was mixed with the supernatant to obtain a secondary product.

(9) (3) The secondary product was stirred in thermostated water bath with a temperature of 20° C. at a shear velocity of 10 s.sup.−1 for 300 min to obtain a tertiary product.

(10) (4) Distilled water was added to the tertiary product with a solid-liquid ratio of 1:1 and stirred for 10 min to precipitate lignin, and the mixed solution containing the precipitate was fed to a filter membrane device and filtered through a filter membrane with molecular weight cut-off of 1,000 to obtain a cut-off precipitate.

(11) (5) The cut-off precipitate was washed and then dried in a vacuum oven to obtain a lignin product with the solid content of over 85%.

Example 3

(12) (1) Crude high boiling solvent (1,4-butanediol) lignin was added to ethanol with a mass concentration of 95%, and ultrasonic vibration was performed at 80° C. for 10 min to obtain a primary product with a lignin mass concentration of 30%.

(13) (2) The primary product was centrifuged at a rotation speed of 15,000 r/min to obtain a supernatant and a solid precipitate, the solid precipitate was washed and filtered with ethanol with a mass concentration of 95%, and the resultant filtrate was mixed with the supernatant to obtain a secondary product.

(14) (3) The secondary product was stirred in thermostated water bath with a temperature of 80° C. at a shear velocity of 1,000 s.sup.−1 for 10 min to obtain a tertiary product.

(15) (4) Distilled water was added to the tertiary product with a solid-liquid ratio of 1:10 and stirred for 1 min to precipitate lignin, and the mixed solution was filtered through a filter membrane with molecular weight cut-off of 5,000 to obtain a cut-off precipitate.

(16) (5) The cut-off precipitate was washed and then dried in a vacuum oven to obtain a lignin product with the solid content of over 85%.

Example 4

(17) (1) Crude acetone lignin was added to diethyl ether with a mass concentration of 100%, and ultrasonic vibration was performed at 20-80° C. for 80 min to obtain a primary product with a lignin mass concentration of 90%.

(18) (2) The primary product was centrifuged at a rotation speed of 6,000 r/min to obtain a supernatant and a solid precipitate, the solid precipitate was washed and filtered with diethyl ether with a mass concentration of 100%, and the resultant filtrate was mixed with the supernatant to obtain a secondary product.

(19) (3) The secondary product was stirred in thermostated water bath with a temperature of 40° C. at a shear velocity of 500.sup.−1 for 100 min to obtain a tertiary product.

(20) (4) Distilled water was added to the tertiary product with a solid-liquid ratio of 1:3 and stirred for 8 min to precipitate lignin, and the mixed solution was filtered through a filter membrane with molecular weight cut-off of 8,000 to obtain a cut-off precipitate.

(21) (5) The cut-off precipitate was washed and then dried in a vacuum oven to obtain a lignin product with the solid content of over 85%.

Example 5

(22) (1) Crude ethylene glycol lignin was added to ethyl acetate with a mass concentration of 100%, and ultrasonic vibration was performed at 60° C. for 100 min to obtain a primary product with a lignin mass concentration of 80%.

(23) (2) The primary product was centrifuged at a rotation speed of 20,000 r/min to obtain a supernatant and a solid precipitate, the solid precipitate was washed and filtered with ethyl acetate with a mass concentration of 100%, and the resultant filtrate was mixed with the supernatant to obtain a secondary product.

(24) (3) The secondary product was stirred in thermostated water bath with a temperature of 60° C. at a shear velocity of 500.sup.−1 for 100 min to obtain a tertiary product.

(25) (4) Distilled water was added to the tertiary product with a solid-liquid ratio of 1:8 and stirred for 5 min, and the mixed solution was filtered through a filter membrane with molecular weight cut-off of over 1,000 to obtain a cut-off precipitate.

(26) (5) The cut-off precipitate was washed and then dried in a vacuum oven to obtain a lignin product with the solid content of over 85%.

Comparative Example 1

(27) Compared with Example 1, the conditions were the same as those in Example 1 except that the step of ultrasonic vibration was eliminated.

Comparative Example 2

(28) Compared with Example 2, the conditions were the same as those in Example 2 except that the step of stirring in thermostated water bath was eliminated.

Comparative Example 3

(29) Compared with Example 3, the conditions were the same as those in Example 3 except that the step of centrifugal filtration was eliminated.

Comparative Example 4

(30) Compared with Example 1, the conditions were the same as those in Example 1 except that acetic acid was replaced with methanol.

Comparative Example 5

(31) Compared with Example 4, the conditions were the same as those in Example 4 except that the filtering through a filter membrane was eliminated.

Comparative Example 6

(32) Compared with Example 5, the conditions were the same as those in Example 5 except that after the solution was prepared in step (1), the operation of stirring in thermostated water bath in step (3) preceded the operation of ultrasonic vibration in step (1).

(33) Experiment Test

(34) The purity, yield and ash content of the purified lignin obtained in Examples and Comparative Examples were tested.

(35) The yield was calculated from the absolute dry weight before and after purification. The purity was tested by ultraviolet spectrophotometry or infrared spectrophotometry. The ash content test was consisting of calculating the ash content after calcination at 800° C. for 3 h.

(36) The results are shown in Table 1.

(37) TABLE-US-00001 TABLE 1 Samples Yield % Ash % Purity % Example 1 82 0.3 92 Example 2 85 0.8 95 Example 3 81 0.4 93 Example 4 82 0.5 91 Example 5 84 0.7 94 Comparative example 1 71 1.5 75 Comparative example 2 70 1.8 62 Comparative example 3 51 1.9 53 Comparative example 4 75 1.6 41 Comparative example 5 70 2.0 45 Comparative example 6 65 1.8 43

(38) It can be learned from Table 1 that, Examples 1-5 where the crude lignin extracted using the organic solvent was purified in accordance with the technical solution provided in the present application, exhibited a yield above 80%, a product purity above 90%, and low ash content. In contrast, in the Comparative Examples 1, 2, 3 and 5 where any of these steps was eliminated, in Comparative Example 4 where a purification solvent other than those of the present application was used, and in Comparative Example 6 where the purification steps is in a sequence other than that of the present application, the purity and the yield of the product are significantly reduced, and the ash content is increased, so that the product is not suitable for downstream application, and the purpose of purification is not achieved. Therefore, the steps of the purification method provided in the present application are indispensable and in unchangeable sequence, and must coordinate with each other in order to achieve the efficient purification.

(39) In summary, the present application provides a method for purifying lignin. In the method, lignin that has been extracted from a plant fiber raw material by an organic solvent process is added to a specified solvent, and is purified by sequentially performing the steps of ultrasonic vibration, centrifugal filtration, stirring in thermostated water bath, and membrane filtration and drying, with the steps being indispensable and in unchangeable sequence. With a synergistic effect achieved by efficient coordination between these steps, the method allows significant impurity removal from lignin and remarkably improved lignin purity while maintaining a high purification yield, and thus indicates broad application prospects and huge market value.

(40) The applicant has stated that although the detailed method of the present application is described through the examples described above, the present application is not limited to the detailed method described above, which means that implementation of the present application does not necessarily depend on the detailed method described above.