FI129825B

FI129825B - Extraction of extractives from lignin

Info

Publication number: FI129825B
Application number: FI20205331A
Authority: FI
Inventors: Laura Kupiainen; Maija Rouhiainen; Päivi Rousu; Sirpa Peltola
Original assignee: Chempolis Oy
Priority date: 2020-03-31
Filing date: 2020-03-31
Publication date: 2022-09-15
Also published as: FI20205331A1; WO2021198556A1

Abstract

The invention relates to a method of extracting extractives from a solid lignin fraction, comprising extracting a solid lignin fraction comprising extractives with an organic solvent to provide an organic extract containing the extractives.

Description

EXTRACTION OF EXTRACTIVES FROM LIGNIN

FIELD OF THE INVENTION The present invention relates to a method of extracting extractives from a solid lignin fraction. More particularly, the invention relates to a method of ex- — tracting extractives from a solid lignin fraction which is derived from a dissolved lignin in a cooking liquor used in an organosolv pulping of a lignocellulosic mate- rial.

BACKGROUND OF THE INVENTION In organosolv pulping method, lignin is extracted from a lignocellulosic material by using an organic solvent as a cooking liquor. Lignin, hemicellulose and extractives dissolve into the cooking liquor while cellulose is recovered as a solid fraction. Various organic solvents including alcohols and acids and combinations thereof have been used in the organosolv pulping. A cooking liquor may contain, for example, formic acid and acetic acid and water.

Lignin may be separated from hemicellulose and extractives present in the cooking liquor by adding water to the cooking liquor. Addition of water pro- duces a lignin precipitate which can be separated from the liquid cooking liquor.

US 2016/0032525 A1 discloses a process for isolating lignin from an aqueous solution containing lignin and non-lignin components. The process in- volves adding a solvent to the aqueous solution. The resultant mixture is filtered whereby lignin is retained by the filter. The retained lignin is mixed with water. The steps of adding a solvent and filtering are repeated until lignin is isolated from non-lignin components. Excess water is removed.

N BRIEF DESCRIPTION OF THE INVENTION N 25 It was found in the present invention that during the lignin precipita- s tion, a portion of extractives are selectively precipitated among lignin. It was fur- 0 ther found that the precipitated extractives may be extracted from the lignin pre- I cipitate with an organic solvent. An object of the present invention is to provide a method of extracting o 30 extractives from a solid lignin fraction, comprising extracting a solid lignin fraction 3 comprising extractives with an organic solvent to provide an organic extract con- O taining the extractives.

The present invention provides a method for recovering valuable ex-

tractives present in a lignocellulosic material which may be appropriately em- ployed in various applications, such as in medicines and in food industry. It was surprisingly found that triterpenyl compounds, for example, which are valuable compounds in medical applications, were found only in the or- ganic extract and notin a liquid cooking liquor containing hemicellulose. Also, val- uable sterol and stanol compounds could be recovered from the solid lignin frac- tion. This shows that at least a portion of extractives are precipitated together with lignin when an aqueous solution is added to cooking liquor after pulping of a ligno- cellulosic material.

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the solid lignin fraction is obtained by precip- itating dissolved lignin of the cooking liquor used in an organosolv pulping of a lig- nocellulosic material. Any lignocellulosic material suitable for organosolv pulping can be used in the invention. The lignocellulosic material may be, for example, soft- wood or hardwood, such as birch. Herbaceous plants, such as common reed or reed canary grass pulp, may also be used. Further, agricultural waste materials, such as straw and bagasse, is applicable. In an embodiment, the lignocellulosic material is biomass of wheat straw, rice straw or bagasse, without limiting thereto. In an embodiment, the cooking liquor contains formic acid, acetic acid, furan compound(s) including furfural, and water. In an embodiment, the amount of formic acid of the solvent is in the range of about 30% to about 75% by weight of the solvent. In another embodiment, the amount of formic acid of the solvent is in the range of about 40% to about 55% by weight. In an embodiment, the amount of acetic acid in the solvent is in the range of about 6% to about 55% by weight of — the solvent. In an embodiment, the amount of water in the organic solventis in the N range of about 13% to about 22% by weight. In an embodiment, the total amount N of furan compounds of the solvent is in the range of about 0.01 to about 3% by 3 weight. 2 In an embodiment, the density of the organic solvent is in the range of E 30 about 1.1 g/cm? to about 1.2 g/cm3. — In an embodiment, the organosolv pulping is carried out at a tempera- O ture range of about 105°C to about 170°C. In another embodiment, the pulping is S carried outat about 120°C to about 165°C. In a further embodiment, the pulping is N carried out at about 130°C to about 160°C.

After cooking, cellulose is separated as a solid fraction from cooking lig- uor while lignin, hemicellulose and extractives remain in the cooking liquor. The dry matter content of the lignin-containing cooking liquor is typi- cally in the range of about 0.5% to about 12%. Alternatively, the lignin-containing cooking liquor is concentrated to a dry matter content of about 5% to about 85%. In an embodiment, the dry matter is in the range of 20% to about 80%. In another embodiment, the dry matter is in the range of about 50% to about 75%. The con- centration may be carried out in any suitable manner, such as by evaporation. Dissolved lignin is precipitated by adding an aqueous solution to the lig- nin-containing cooking liquor. In an embodiment, the aqueous solution is water. The ratio of added aqueous solution with respect to a lignin-containing cooking liquor varies in the range of 0.01:1-4:1 parts by weight. In an embodiment, the ratio varies in the range of 0.3:1-4:1 parts by weight. In another embodiment, the ratio varies from about 1:1 to about 1:2. In a further embodiment, the aqueous — solution is added to the lignin-containing cooking liquor in equal parts by weight, i.e. 1:1. In a further embodiment, the aqueous solution is added to the lignin-con- taining cooking liquor in a weight ratio of 1:2. The lignin precipitate is separated from the cooking liquor. The separa- tion may be carried out by any convenient manner, including filtration, such as a pressure filter or a membrane filter, a separator or a centrifuge, such as a decanter centrifuge. Various combinations of the separation methods may also be employed. In an embodiment, the separation is carried out by filtration. The lignin precipitate is then extracted with an organic solvent. In an embodiment, the organic solvent is acetone. The following examples are presented for further illustration of the in- N vention without limiting the invention thereto.

N N Example 1 S Wheat straw was delignified at a cooking temperature of 135°C for 35 2 minutes with a cooking liquor containing 51 wt-% of formic acid, the rest being E 30 acetic acid, water and furfural. The density of the cooking liquor was 1.14 g/cm3. = The cooking liquor containing lignin was then filtered off from the resultant cellu- A lose pulp. S The lignin-containing cooking liguor was mixed with water in a weight N ratio 1:1 whereby a solid lignin precipitate was formed. The precipitated lignin was filtered off with a glass fiber filter with a pore size of 0.6 um and left at room tem- perature until dried.

The lignin precipitate was extracted with acetone.

The extractives of the acetone solution were analysed by gas chroma- tography. The results are shown in Table 1. Example 2 Wheat straw was delignified at a cooking temperature of 130°C for 20 minutes with a cooking liquor containing 41 wt-% of formic acid, the rest being acetic acid, water and furfural. The density of the cooking liquor was 1.125 g/cm3.

The cooking liquor containing lignin was then filtered off from the resultant cellu- lose pulp. The dry matter content of the cooking liquor was 15%.

The lignin-containing cooking liquor with a dry matter of 15% was mixed with water in a weight ratio 1:1 whereby a solid lignin precipitate was formed. The precipitated lignin was separated with a separator. The resultant su- — pernatant was analysed by gas chromatography. The results are shown in Table 1. Example 3 Bagasse was delignified at a cooking temperature of 141°C for 37 minutes with a cooking liquor containing 51 wt-% of formic acid, the rest being acetic acid, water and furfural. The density of the cooking liquor used for the delig- — nification was 1.14 g/cm3. The cooking liquor containing lignin was then filtered off from the resultant cellulose pulp. The dry matter content of the lignin-contain- ing cooking liquor was 9%.

The lignin-containing cooking liquor with a dry matter of 9% was mixed with water in a weightratio 1:2 whereby a solid lignin precipitate was formed. The N 25 precipitated lignin was separated with a separator. The resultant supernatant was N analysed by gas chromatography. The results are shown in Table 1. £ o Table 1. = 2

S 2 c6 | 26 | 09 | 23

C18:0H C18:2 C18:1 C18:3 C18:0 Sandaraco <0.01 <0.01 13 Pimaric acid etic acid C20:3 Abietic Acid C22:0 0.044 C23:0 0.087 0.038 C24:0 0.064 0.011 Cholesterilene 0.012 cloartenol lupeol | 06 | <001 [| <0.01 | Methylbetulinate | 006 | ~~ <001 | <001 — |

A S

N 7 zoic acid 2 z a 0.029 = 0.042 D Table 1 shows that valuable triterpenyl compounds are selectively N 5 boundtolignin precipitate, i.e. are detected in the acetone extract derived from the N lignin precipitate. Sterols and stanols are partly bound to the lignin precipitate and recovered in the extract.

Claims

1. A method of extracting extractives from a solid lignin fraction, com- prising extracting a solid lignin fraction comprising extractives with an organic sol- vent to provide an organic extract containing the extractives comprising triterpenyl compounds.

2. The method of claim 1, wherein the organic solvent is acetone.

3. The method of claim 1 or 2, wherein the solid lignin fraction is a lignin precipitate derived from an organosolv pulping of a lignocellulosic material.

4. The method of claim 3, wherein the lignin precipitate is obtained by adding an aqueous solution to a lignin-containing cooking liquor used in the orga- nosolv pulping, containing dissolved lignin.

5. The method of claim 4, wherein the aqueous solution is added to the lignin-containing cooking liquor in a weight ratio varying in the range of 0.01:1- 4:1 parts by weight, specifically in the range of 0.3:1-4:1 parts by weight, more specifically from about 1:1 to about 1:2.

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