Polyacid dispersants from lignin

Valorizating lignin has a great potential to contribute to the goal of achieving an economical hydrocarbon biofuel.  We describe a method to treat lignin using a room-temperature, one-step oxidative process to selectively open the aromatic rings and generate carboxylic acid groups. The approach specifically avoids ether bond cleavage and depolymerization to generate a polymeric dispersant that constitutes a valuable product without need for further upgrading.  Polymeric dispersants are used extensively in dyes, paints, concrete, pharmaceuticals, cosmetics, paper and paperboard, ceramics processing, and to inhibit fouling in cooling water systems.  The approach uses chelator-mediated Fenton chemistry (e.g., FeCl₃ + chelator + H₂O₂) or Fe-containing Metal-Organic Framework (MOF) catalysts.   The Fenton reaction is used to treat industrial waste and organic contaminants in groundwater and has been employed in biomass pretreatment strategies.   We show that use of an Fe chelator in the Fenton system leads to substantially higher yields of solubilized polyacid product per oxidant (H₂O₂) consumed.   We also show that the amount of ring opening can be controlled by the reaction conditions.  By controlling the extent of ring opening, the relative amounts of hydrophobic and charged groups can be tailored to produce dispersants with properties optimized for specific applications. The economic feasibility of this process depends on maximizing the yield of solubilized lignin material per amount of H₂O₂ consumed.  We will describe progress in that regard and the best results achieved to date.  We will also show that the material solublized by this reaction behaves as an effective dispersant.