Digestion of cellulosic biomass solids may be complicated by release of lignin therefrom. Methods and systems for processing a reaction product containing lignin-derived products, such as phenolics, can comprise hydrotreating the reaction product to convert the lignin-derived products to desired higher molecular weight compounds. The methods can further include separating the higher molecular weight compounds from unconverted products, such as unconverted phenolics, and recycling the unconverted phenolics for use as at least a portion of the digestion solvent and for further conversion to desired higher molecular weight compounds with additional hydrotreatment. The methods and systems can further include generating hydrogen with the further hydrotreatment.

A process for recovery of lignin from black liquor that contains either soluble or dispersed lignin by generating a “liquid lignin” at high yield is disclosed. Soluble lignin at a high pH is precipitated by reducing the pH of the black liquor stream by countercurrent reaction with carbon dioxide, at elevated temperature and pressure, creating a dense liquid-lignin phase and a light lignin-depleted phase. The dense lignin-rich phase is separated and washed countercurrently with a non-sulfur containing acid, such as acetic acid or formic acid, to displace metal cations from the lignin, creating a low-salt lignin, which is then formed into a low-dust, high-bulk density lignin fuel pellet. If desired, an oxidation step may be used to eliminate odor for lignins having high value green chemistry applications.

The invention herein disclosed and claimed is a process for refining fiber from lignocellulosic biomass. The process provides refined fiber and agriculturally amenable co-products, with a virtually waste-free systems design.

Digestion of cellulosic biomass solids may be complicated by release of lignin therefrom. Methods and systems for processing a reaction product containing lignin-derived products, such as phenolics, can comprise hydrotreating the reaction product to convert the lignin-derived products to desired higher molecular weight compounds. The methods can further include separating the higher molecular weight compounds from unconverted products, such as unconverted phenolics, and recycling the unconverted phenolics for use as at least a portion of the digestion solvent and for further conversion to desired higher molecular weight compounds with additional hydrotreatment.

Lignin has a weight average molecular weight of at least 6,000 daltons and comprising (a) from 2% to 10% of a low molecular component having a weight average molecular weight (M.sub.w) of from 300 to 1500 daltons, and (b) from 10% to 50% of a high molecular weight component having a weight average molecular weight (M.sub.w) of at least 10,000 daltons; and exhibiting a T.sub.g of from 100° C. to 130° C. when measured by differential scanning calorimetry.

The invention is directed to compositions and processes concerning efficient downstream processing of products derived from organic acids pretreatment of plant materials.

The method is for separation of lignin from original black liquor (BL.sub.IN) that has a first precipitation phase (PR1/PR2) for precipitation of lignin by a first acidification using acidifier, CO.sub.2, at alkaline conditions, then separating a lignin cake with subsequent suspension of the lignin cake in a strong acid in order to leach out metals from the lignin followed by dewatering and obtaining a clean lignin product LP. Lignin germ particles (LG) are added to the original black liquor in the first precipitation stage, preferably between two phases in said precipitation stage, in order to increase lignin particle growth on such lignin germ particles instead of spontaneous nucleation of lignin particles in said original black liquor. This results in improved filterability in subsequent dewatering and lignin cake formation and hence an increased lignin yield.

The method is for separation of lignin from original black liquor (BL.sub.IN) that has a first precipitation phase (PR1/PR2) for precipitation of lignin by a first acidification using acidifier, CO.sub.2, at alkaline conditions, then separating a lignin cake with subsequent suspension of the lignin cake in a strong acid in order to leach out metals from the lignin followed by dewatering and obtaining a clean lignin product LP. Lignin germ particles (LG) are added to the original black liquor in the first precipitation stage, preferably between two phases in said precipitation stage, in order to increase lignin particle growth on such lignin germ particles instead of spontaneous nucleation of lignin particles in said original black liquor. This results in improved filterability in subsequent dewatering and lignin cake formation and hence an increased lignin yield.

A process for recovering carbonized lignin having a defined grain size distribution from a lignin-containing liquid is provided. The lignin-containing liquid is subjected to a hydrothermal carbonization to convert the lignin into a carbonized lignin and the carbonized lignin is separated from the liquid containing the carbonized lignin. The lignin-containing liquid is subjected to a hydrothermal carbonization at temperatures in the range from about 150° C. to about 280° C. and by adapting the H+ ion concentration in the lignin-containing liquid before and/or during the hydrothermal carbonization the grain size distribution of the carbonized lignin is adjusted.

A process for recovering carbonized lignin having a defined grain size distribution from a lignin-containing liquid is provided. The lignin-containing liquid is subjected to a hydrothermal carbonization to convert the lignin into a carbonized lignin and the carbonized lignin is separated from the liquid containing the carbonized lignin. The lignin-containing liquid is subjected to a hydrothermal carbonization at temperatures in the range from about 150° C. to about 280° C. and by adapting the H+ ion concentration in the lignin-containing liquid before and/or during the hydrothermal carbonization the grain size distribution of the carbonized lignin is adjusted.