By exploiting the novel liquid–liquid equilibrium that exists between lignin and hot, one-phase solutions of aqueous renewable solvents, crude bulk lignins can be simultaneously fractionated, cleaned, and solvated for conversion to high-value, high-quality bioproducts.  This unusual phase behavior forms the basis for the ALPHA (Aqueous Lignin Purification with Hot Agents) process.  With ALPHA, control of the purity, molecular weight, and chemical functionality of lignin becomes possible.  In particular, lower molecular weight (MW) lignins and impurities are extracted into the solvent-rich phase, and higher MW lignins are solvated and purified of impurities in the polymer-rich phase.  Phase-transition temperatures from solid–liquid to the desired liquid–liquid equilibrium have been measured for mixtures of Kraft lignins with aqueous solutions of methanol, ethanol, isopropanol, acetic acid, and acetone.  Furthermore, the global phase behavior exhibited by these systems has been measured for selected (pseudo-)ternaries, including the lignin–acetone–water and lignin–acetic acid–water systems.  Two examples of how the LLE region exhibited by these systems facilitates materials applications will be presented: (1) By using the solvated, polymer-rich phase, the continuous dry-spinning of high MW lignin fractions into micron-sized fibers is made possible.  These fibers were subsequently converted into low-cost carbon fibers almost 40% stronger than any lignin-based carbon fiber reported to date. (2) Low MW lignins were isolated by a two-stage process that first uses the solvent-rich phase to isolate a low MW lignin fraction; that fraction is then purified by transferring it to the polymer-rich phase.  The resultant lignin was subsequently used to create dispersions for coating applications.

Exploiting the phase behavior of lignin with renewable aqueous solvents: Enabling higher-value applications

2019 Fall National Meeting

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