Separation of lignin and sugars from biomass pre-treatment liquors
The invention relates to an improved process for separating lignin and monomeric sugars from a liquor comprising lignin and monomeric sugars in a solvent mixture of water and at least one organic solvent, which employs membrane filtration techniques such as nanofiltration and selective water removal, preferably by permeation through a membrane which is selective for water molecules. The invention further relates to a modular system for executing the process according to the invention. The process and system according to the invention are particularly suitable to be incorporated with pre-treatment of lignocellulosic biomass, in particular by organosolv fractionation or solvolysis.
1. A process for separating lignin and monomeric sugars from a biomass pre-treatment liquor comprising lignin and monomeric sugars in a solvent mixture comprising water and an organic solvent, the process comprising:
(a) subjecting the liquor to nanofiltration over a membrane capable of retaining lignin and permeating monomeric sugars; and
(b) subjecting a permeate originating from step (a) to selective water removal to obtain a suspension comprising precipitated monomeric sugars;
(c) precipitating lignin from a retentate originating from step (a), and
(d) isolating precipitated monomeric sugars from the suspension of step (b).
2. The process according to claim 1 , wherein the liquor is an organosolv liquor or a solvolysis liquor.
3. The process according to claim 1 , wherein the liquor is an organosolv liquor.
4. The process according to claim 2 , wherein the organosolv liquor is obtained by subjecting a lignocellulosic biomass to organosolv prior to step (a).
5. The process according to claim 4 , wherein the organosolv is performed using a ketone organic solvent.
6. The process according to claim 5 , wherein the ketone organic solvent is acetone.
7. The process according to claim 1 , wherein the liquor has a temperature of 100 - 280° C. at the beginning of step (a).
8. The process according to claim 1 , wherein the nanofiltration membrane has a molecular weight cut-off of 200 - 2500 Da.
9. The process according to claim 8 , wherein the nanofiltration membrane has a molecular weight cut-off of 300 - 2000 Da.
10. The process according to claim 1 , wherein the selective water removal is accomplished by selective permeation using a membrane selective for permeation of water molecules.
11. The process according to claim 10 , wherein the selective permeation is accomplished by vapour permeation.
12. The process according to claim 10 , wherein the membrane selective for permeation of water molecules comprises organosilane moieties represented by Si p O q ((CH 2 ) n ) r , wherein n=1−7, p=1.6 −2.4, q =2.5−3.5, and r =0.6 −1.4.
13. The process according to claim 1 , which does not comprise active cooling and/or heating a solution or suspension.
14. The process according to claim 1 , which does not comprise a distillation step.