Methods for preparing thermally stable lignin fractions

1. A lignin composition comprising lignin, wherein the composition is characterized by a consistent glass transition temperature (Tg) as determined by two consecutive differential scanning calorimetry (DSC) runs of the same lignin portion according to DIN 53765-1994, wherein a first Tg is measured during a first DSC run, a second Tg is measured during a second DSC run, and the difference between the first Tg and the second Tg is less than 10° C.

2. The composition of claim 1 , wherein the difference between the first Tg and the second Tg is less than 5° C.

3. The composition of claim 1 , wherein the second glass transition temperature is above 160° C.

4. The composition of claim 1 , wherein the second glass transition temperature is below 100° C.

5. The composition of claim 1 , further comprising a marker molecule at a concentration of at least 100 ppb.

6. The composition of claim 5 , wherein the marker molecule is selected from the group consisting of isopropanol, ethyl acetate, ethyl formate, dichloromethane, hexanol, furfural, hydroxy-methyl furfural, 2,3,5 trimethyl furan, p-hydroxyphenoxyacetic acid, 4-hydroxy-3,5-dimethoxyphenyl acetic acid, methylethyl ketone, methylpropenyl ketone, 3-(2-furyl)-3-penten-2-one, 3-methyl-2-penten-4-one, 3,4-dimethyl-4-hexene-one, 5-ethyl-5-hexene-3-one, 5-methyl-4-heptene-3-one, o-hydroxyanisole, 3-ethyl-4-methyl-3-penten-2-one, 3,4,4-trimethyl-2-cyclohexene-1-one, 2′-hydroxy-4′,5′-dimethylacetophenone, 1-(4-hydroxy-3-methoxyphenyl)propane, methanol, galacturonic acid, dehydroabietic acid, glycerol, fatty acids and resin acids.

7. The composition of claim 1 , further comprising volatile sulfur compounds in an amount less than 0.1 times an amount found in Kraft lignin.

8. The composition of claim 1 , further comprising ash in an amount less than 0.5%.

9. The composition of claim 1 , further comprising sulfur in an amount less than 700 ppm.

10. The composition of claim 1 , further comprising soluble carbohydrates in an amount less than 0.5%.

11. A method for fractionating lignin, the method comprising:

(i) contacting a sample comprising solid lignin and less than 1% weight/weight carbohydrates with an organic solvent to form a biphasic mixture, wherein the mixture comprises:

(a) a remainder solid comprising a first fraction of the lignin, wherein the first fraction is designated as a solvent-insoluble lignin fraction; and

(b) a liquid solution comprising the solvent and a second fraction of the lignin, wherein the second fraction is designated as a solvent-soluble lignin fraction; and

(ii) spatially separating the solvent-insoluble lignin fraction from the solvent-soluble lignin fraction;

wherein the solvent-insoluble lignin fraction and the solvent-soluble lignin fraction have different glass transition temperatures.

12. The method of claim 11 , wherein the solvent comprises at least one organic molecule having up to 5 carbon atoms and at least one heteroatom.

13. The method of claim 11 , wherein the contacting occurs at 20 to 50° C.

14. The method of claim 11 , wherein the contacting occurs for 1 to 10 hours.

15. The method of claim 11 , wherein the spatial separating comprises filtration or decantation of the solvent from the solvent-insoluble lignin fraction.

16. The method of claim 11 , further comprising evaporating the solvent from the solvent-soluble lignin fraction and drying each fraction to obtain a dry solid solvent-soluble lignin fraction and a dry solid solvent-insoluble lignin fraction;

wherein the two dry solid lignin fractions have different molecular weights as determined by gel permeation chromatography and different glass transition temperatures.

17. The method of claim 11 , wherein at least one of the lignin fractions has a consistent glass transition temperature (Tg) as determined by two consecutive differential scanning calorimetry (DSC) runs of the same lignin portion according to DIN 53765-1994, wherein a first Tg is measured during a first DSC run, a second Tg is measured during a second DSC run, and the difference between the first Tg and the second Tg is less than 10° C.

18. The method of claim 11 , wherein the solvent-soluble lignin fraction has a different glass transition temperature than the solvent-insoluble lignin fraction.

19. The method of claim 11 , wherein the solvent is selected from a group consisting of methanol, ethanol, isopropanol, ethyl acetate, ethyl formate, dichloromethane, and any mixture thereof.

20. A method for producing high purity lignin from a biomass, comprising:

(i) removing hemicellulose sugars from the biomass, thereby obtaining a lignin-containing remainder; wherein the lignin-containing remainder comprises lignin and cellulose;

(ii) contacting the lignin-containing remainder with a lignin extraction solution to produce a lignin extract and a cellulosic remainder; wherein the lignin extraction solution comprises a limited-solubility solvent, an organic acid, and water, wherein the limited-solubility solvent and the water form an organic phase and an aqueous phase; and

(iii) separating the lignin extract from the cellulosic remainder; wherein the lignin extract comprises lignin dissolved in the limited-solubility solvent;

and further comprising one, two, three or four additional step(s) selected from:

(iv) distilling or flash evaporating the lignin extract, thereby removing the bulk of the limited-solubility solvent from the lignin extract to obtain a solid lignin;

(v) heating the solid lignin, thereby removing trace limited-solubility solvent or water from the solid lignin;

(vi) applying a vacuum to the solid lignin, thereby removing trace limited-solubility solvent or water from the solid lignin; and

(vii) contacting the solid lignin with an organic solvent to form a biphasic mixture, wherein the mixture comprises:

(a) a remainder solid comprising a first fraction of the lignin, wherein the first fraction is designated as a solvent-insoluble lignin fraction; and

(b) a liquid solution comprising the solvent and a second fraction of the lignin, wherein the second fraction is designated as a solvent-soluble lignin fraction.