Valorization Of Lignin In Municipal Solid Waste For Biobased Polymer Synthesis And Its Future Applications

Abstract

In 2018, Americans generated about 292 million metric tons of Municipal Solid Waste (MSW), with more than 146 million tons of waste discarded into landfills. As MSW is approximately 63% lignocellulosic biomass, it can be used as a feedstock for the production of biobased chemicals and materials. However, the heterogeneity of MSW makes it challenging to upgrade by most conventional processes. This work leverages process intensification to valorize MSW in a lignin-first approach, reactive distillation-reductive catalytic fractionation (RD-RCF). In RD-RCF, lignin is concurrently separated from cellulosics and other components of MSW (e.g., plastic waste), and depolymerized to phenolic compounds. The products are distilled as they form, greatly simplifying separations by eliminating the need to extract products from such a complex and contaminated reaction mixture. Two different conditions were analyzed: ruthenium on carbon catalyst and no catalyst. The distilled phenolic products were analyzed using gas chromatography-mass spectrometry to determine composition and yield. An Aspen Plus library of the physical properties commonly seen in lignin depolymerization products was created using group contribution methods and other estimation parameters. As a proof of concept for the applications of depolymerized MSW lignin, a block copolymer was synthesized from acrylated MSW lignin monomers and butyl acrylate. The hydroxy groups of the phenolic compounds were acrylated through esterification with acid chlorides. The functionalized phenolic monomers then were polymerized using a one-pot reversible addition-fragmentation chain-transfer (RAFT) polymerization. The block polymer produced by RAFT polymerization was characterized by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and atomic force microscopy (AFM).