Top Value-Added Chemicals from Biomass - Volume II—Results of Screening for Potential Candidates from Biorefinery Lignin

Abstract

This report evaluates lignin’s role as a renewable raw material resource. Opportunities that arise from utilizing lignin fit into one of three categories: 1)power, fuel and syngas (generally near-term opportunities) 2) macromolecules (generally medium-term opportunities) 3) aromatics and miscellaneous monomers (long-term opportunities). Biorefineries will receive and process massive amounts of lignin. For this reason, how lignin can be best used to support the economic health of the biorefinery must be defined. An approach that only considers process heat would be shortsighted. Higher value products present economic opportunities and the potential to significantly increase the amount of liquid transportation fuel available from biomass. In this analysis a list of potential uses of lignin was compiled and sorted into “product types” which are broad classifications (listed above as power—fuel—syngas; macromolecules; and aromatics). In the first “product type” (power—fuel—gasification) lignin is used purely as a carbon source and aggressive means are employed to break down its polymeric structure. In the second “product type” (macromolecules) the opposite extreme is considered and advantage of the macromolecular structure imparted by nature is retained in high-molecular weight applications. The third “product type” (aromatics) lies somewhere between the two extremes and employs technologies that would break up lignin’s macromolecular structure but maintain the aromatic nature of the building block molecules. The individual opportunities were evaluated based on their technical difficulty, market, market risk, building block utility, and whether a pure material or a mixture would be produced. Unlike the “Sugars Top 10” report it was difficult to identify the ten best opportunities, however, the potential opportunities fell nicely into near-, medium- and long-term opportunities. Furthermore, the near-, medium- and long-term opportunities roughly align with the three “product types.” From this analysis a list of technical barriers was developed which can be used to identify research needs. Lignin presents many challenges for use in the biorefinery. Chemically it differs from sugars having a complex aromatic substructure. Unlike cellulose, which has a relatively simple substructure of glucose subunits, lignin has a high degree of variability in its structure which differs both from biomass source and from the recovery process used. In addition to its variability lignin is also reactive and to some degree less stable thermally and oxidatively to other biomass streams. What this means is that integrating a lignin process stream within the biorefinery will require identifying the best method to separate lignin from biomass cost-effectively.