Solvent and recovery process for lignin
Methods for obtaining purified lignin and the lignin that can be obtained by the methods are described. Methods include processing pretreated lignocellulosic biomass feedstock to recover the lignin and provide a lignin composition with a very low level of impurities such as metals and ash. In addition, the lignin recovered from the process can have a narrow molecular weight distribution and, depending upon the specific stages utilized in the process, can have a predetermined molecular weight. The process includes one or more separation stages in which a lignin-containing feedstock is mixed with a solvent solution. The mixture fractionates to form a solvent-rich liquid phase and a lignin-rich liquid phase, the lignin being partitioned across the phases according to the molecular weight of the lignin. Furthermore, the metal salts of the pretreated lignocellulosic biomass feedstock also partition across the phases.
1. A method for recovering lignin comprising:
combining a pretreated lignocellulosic biomass feedstock containing lignin with a single phase solvent solution to form a mixture, the single phase solvent solution comprising a solvent selected from water, a C 1 to C 4 organic acid, an aliphatic alcohol, a ketone, or a combination thereof;
stirring and optionally heating the mixture;
following the combination and optional heating, the lignin solvating into the single-phase solvent solution and the mixture separating into a solvent-rich liquid phase and a lignin-rich liquid phase, wherein the solvent-rich liquid phase comprises a first portion of the solvated lignin in a liquid form and a first portion of the solvent and the lignin-rich liquid phase comprises a second portion of the solvated lignin in a liquid form and a second portion of the solvent, the solvated lignin of the first portion differing from the solvated lignin of the second portion, the second portion of the solvent being from 50% to 70% by weight of the lignin-rich liquid phase, the ratio of the first portion of the solvent to the first portion of the solvated lignin being greater than the ratio of the second portion of the solvent to the second portion of the solvated lignin;
separating the solvent-rich liquid phase from the lignin-rich liquid phase; and
recovering the solvated lignin of the solvent-rich liquid phase and/or the solvated lignin of the lignin-rich liquid phase.
2. The method of claim 1 , wherein the average number average molecular weight of the first portion of the lignin differs from the average number average molecular weight of the second portion of the lignin.
3. The method of claim 1 , further comprising one or more additional stages during which a lignin-containing stream from a previous stage is combined with another solvent solution to form a mixture and wherein upon this combination optionally with heating the mixture separates to form another solvent-rich liquid phase and another lignin-rich liquid phase.
4. A method for recovering lignin comprising:
combining a pretreated lignocellulosic biomass feedstock containing lignin and one or more additional components with a single phase solvent solution to form a mixture, the single phase solvent solution including water and a solvent, wherein the solvent comprises a C 1 to C 4 organic acid, an aliphatic alcohol, a ketone, or a combination thereof;
stirring and heating the mixture to a temperature of about 50° C. or greater;
following the combination, stirring and heating, the lignin solvating into the solvent solution and the mixture separating into a solvent-rich liquid phase and a lignin-rich liquid phase, wherein the solvent-rich liquid phase comprises a first portion of the lignin as solvated lignin in a liquid form and the lignin-rich liquid phase comprises a second portion of the lignin as solvated lignin in a liquid form, each of the solvent-rich liquid phase and the lignin-rich liquid phase comprising water, the solvent and one or more components of the lignocellulosic biomass feedstock, the solvated lignin of the solvent-rich liquid phase differing from the solvated lignin of the lignin-rich liquid phase;
separating the solvent-rich liquid phase from the lignin-rich liquid phase; and
recovering the solvated lignin of the solvent-rich liquid phase and/or the solvated lignin of the lignin-rich liquid phase.
5. The method of claim 4 , wherein the solvent comprises acetic acid.
6. The method of claim 4 , wherein the solvent comprises a ketone.
7. The method of claim 4 , wherein the average number average molecular weight of the first portion of the lignin differs from the average number average molecular weight of the second portion of the lignin.
8. The method of claim 4 , wherein the first portion of the lignin and/or the second portion of the lignin have a narrower molecular weight distribution as compared to the molecular weight distribution of the lignin of the pretreated lignocellulosic biomass feedstock.
9. The method of claim 4 , the pretreated lignocellulosic biomass feedstock comprising metal, the metals content of the solvent-rich liquid phase differing from the metals content of the lignin-rich liquid phase.
10. The method of claim 9 , the lignin-rich liquid phase comprising 50% or less by weight of the metal of the pretreated lignocellulosic biomass feedstock.
11. The method of claim 4 , the pretreated lignocellulosic biomass feedstock having an ash content, the ash content of the solvent-rich liquid phase differing from the ash content of the lignin-rich liquid phase.