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, hemiceliulose 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 hemiceliulose 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.

BRIEF DESCRIPTION OF THE INVENTION

It was found in the present invention that during the lignin precipita tion, a portion of extractives are selectively precipitated among lignin. It was fur ther found that the precipitated extractives may be extracted from the lignin pre cipitate with an organic solvent.

An object of the present invention is to provide 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 con 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 not in a liquid cooking liquor containing hemiceliulose. 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 solvent is in the range of about 13% to about 22% by weight. In an embodiment, the total amount of furan compounds of the solvent is in the range of about 0.01 to about 3% by weight.

In an embodiment, the density of the organic solvent is in the range of about 1.1 g/cm ³ to about 1.2 g/cm ³ .

In an embodiment, the organosolv pulping is carried out at a tempera ture range of about 105°C to about 170°C. In another embodiment, the pulping is carried out at about 120°C to about 165°C. In a further embodiment, the pulping is carried out at about 130°C to about 160°C.

After cooking, cellulose is separated as a solid fraction from cooking liq 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 15%. In an embodiment, the dry matter content is in the range of about 0.5% to about 12%. In another embodiment, the dry matter content is in the range of about 9% to about 15%. 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 concentration 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 vention without limiting the invention thereto.

Example 1

Wheat straw was delignified at a cooking temperature of 135°C for 35 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 was 1.14 g/cm ³ . The cooking liquor containing lignin was then filtered off from the resultant cellu lose pulp.

The lignin-containing cooking liquor was mixed with water in a weight 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 gm 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/cm ³ . 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/cm ³ . 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 weight ratio 1:2 whereby a solid lignin precipitate was formed. The precipitated lignin was separated with a separator. The resultant supernatant was analysed by gas chromatography. The results are shown in Table 1.

The amounts of the extractives in Table 1 are percentages by weight. In "Ex 1, the percentage describes an amount in acetone. In Ex. 2 and Ex. 3, the per centage describes an amount in the supernatant. Table 1.

Table 1 shows that valuable triterpenyl compounds are selectively bound to lignin precipitate, i.e. are detected in the acetone extract derived from the lignin precipitate. Sterols and stands are partly bound to the lignin precipitate and recovered in the extract.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The inven tion and its embodiments are not limited to the examples described above but may vary within the scope of the claims.