Lignin preparations isolated from plant material, and methods for their isolation and use

Abstract

Lignin polymers having distinctive properties, including a generally high molecular weight and generally homogeneous size distribution, as well as preservation of native reactive side groups, are isolated by solvent extraction of plant materials. Methods for isolation of lignin polymers, and for use of the isolated lignin polymers are disclosed. Compositions containing lignin isolated from plant materials, such as carbon fiber composites, resins, adhesive binders and coatings, polyurethane-based foams, rubbers and elastomers, plastics, films, paints, nutritional supplements, food and beverage additives are disclosed. Xylose and xylose derivatives, furfural, fermentable sugars, cellulose and hemi-cellulose products may be used directly or further processed. The lignin polymers and other plant-derived products disclosed herein may be produced in abundance at low cost, and may be used as substitutes for feedstocks originating from fossil fuel or petrochemical sources in the manufacture of various products.

1 . An isolated lignin preparation prepared from a lignocellulosic plant material selected from the group consisting of: woody or herbaceous materials; agricultural or forestry residues; and dedicated energy crops, wherein the isolated lignin preparation is prepared by:
 (a) contacting the lignocellulosic plant material with an aqueous ethanol solution at an elevated temperature and an elevated pressure for a retention time sufficient to produce a liquid solvent mixture comprising ethanol, ethanol-soluble lignin and water, and a plant pulp material;   (b) separating the plant pulp material from the liquid solvent mixture;   (c) precipitating the ethanol-soluble lignin and forming lignin particulates by diluting the liquid solvent mixture with an aqueous gasified solution containing dissolved gas under conditions that promote the formation of gas bubbles, whereby the gas bubbles attach to precipitated lignin particulates as they form, and the precipitated lignin particulates are transported to the liquid surface by attachment to the gas bubbles;   (d) harvesting the precipitated lignin from the liquid surface; and   (e) recovering an isolated lignin preparation from the precipitated lignin.   
     
     
         2 . The isolated lignin preparation of  claim 1 , wherein the lignocellulosic plant material is a coppicable hardwood. 
     
     
         3 . The isolated lignin preparation of  claim 1 , wherein the lignocellulosic plant material comprises material from a  Salix  species. 
     
     
         4 . The isolated lignin preparation of  claim 1 , wherein the isolated lignin preparation has a weight average molecular mass (Mw) of at least about 4,000. 
     
     
         5 . The isolated lignin preparation of  claim 1 , wherein the isolated lignin preparation has a weight average molecular mass (Mw) of at least about 4,500. 
     
     
         6 . The isolated lignin preparation of  claim 1 , wherein the isolated lignin preparation has a weight average molecular mass (Mw) of at least about 5,000. 
     
     
         7 . The isolated lignin preparation of  claim 1 , wherein the isolated lignin preparation has a ratio of syringyl (S) units to guaiacyl (G) units of at least about 1:1. 
     
     
         8 . The isolated lignin preparation of  claim 1 , wherein the isolated lignin preparation has a ratio of syringyl (S) units to guaiacyl (G) units of at least about 3:1. 
     
     
         9 . The isolated lignin preparation of  claim 1 , wherein the isolated lignin preparation comprises less than about 1.0% sugars. 
     
     
         10 . The isolated lignin preparation of  claim 1 , wherein the isolated lignin preparation comprises a high ratio of β-aryl-ether (>50%) and resinol (>8%) subunits. 
     
     
         11 . The isolated lignin preparation of  claim 1 , wherein step (a) is carried out substantially in the absence of an introduced acid or alkaline catalyst. 
     
     
         12 . A material prepared using the isolated lignin preparation of  claim 1 . 
     
     
         13 . A method for recovering lignin from an aqueous suspension of lignin comprising:
 (a) adding to the suspension a component selected from the group consisting of: ethanol at a concentration of less than 40% v/v; ammonium salts other than ammonium bicarbonate; and detergents other than Tween™ 80 or sodium dodecyl sulfate, whereby the lignin flocculates; and   (b) harvesting the flocculated lignin.   
     
     
         14 . An isolated lignin preparation produced using the method of  claim 13 . 
     
     
         15 . A material prepared using the isolated lignin preparation of  claim 14 .