Maleic Acid Hydrotropic Fractionation: Effective Deconstruction of Lignocellulose for Multi-Products Biorefinery

J.Y. Zhu
USDA Forest Products Laboratory,
United States

Keywords: biorefinery, fractionation, co-products, biofuel, enzymatic saccharification, lignocelllulose, cellulose nanomaterials


Producing bioenergy, biochemicals, and biomaterials from renewable plant biomass can achieve a sustainable future through carbon sequestration and reduced use of fossil hydrocarbons. Developing lignocellulose fractionation processes that are not only sustainable, but also yield easily processable building blocks is the key to commercial success. For the past decade, we have devoted our efforts to advance the science and engineering critical to commercialization of biorefining technologies. In this presentation, I will report our recent discovery of hydrotropic properties of a recyclable (low solubility) dicarboxylic acid, maleic acid (MA), for potential low-cost and efficient fractionation of lignocelluloses through rapid dissolution of lignin and hemicelluloses at atmospheric pressure. MA hydrotropic fractionation (MAHF) of wood results in two fractions: (i) a primarily cellulose rich water-insoluble solid (WIS) fraction that can be used for the production of high-value building blocks, such as lignocellulosic nanomaterials, fibers, and/or sugars through subsequent enzymatic hydrolysis; and (ii) a spent acid liquor stream containing hemicellulosic sugars and minimally condensed dissolved lignin that can be easily precipitated by simply diluting the spent acid liquor using water to below the minimal hydrotropic concentration. The dissolved hemicelluloses in the spent liquor can be dehydrated into furans using the MA in the spent liquor after lignin precipitation without additional catalysts. MA can then be reconcentrated, recovered, and reused. Nuclear magnetic resonance analyses revealed that MAHF dissolved lignin (MAHL) has a very high content of -aryl ether linkages with minimal condensation, which facilitated catalytic conversion into monophenols. The MAHF is carboxylated with light color and therefore is suitable for other applications such as sunblock and skincare products. Carboxylation of the residual lignin in the fractionated WIS enhanced enzymatic saccharification by decreasing nonproductive cellulase binding to lignin, as well as facilitated nanofibrillation of WIS for producing lignin-containing cellulose nanofibrils (LCNFs) to substantially decrease fibrillation energy. MA is a FDA-approved indirect food additive (21CFR175-177) and can valorize three major lignocellulose components alone, it therefore has significant advantages for biorefinery applications.