Lignin valorization beyond energy use: has lignin's time finally come?

Abstract

AbstractAccording to an old proverb, ‘you can make anything out of lignin, except money’. The complexity of lignin's structure and many inferior characteristics of lignin, such as its insolubility in organic solvent and poor reactivity related to it large molecular weight, have posed significant challenges to lignin valorization. Driven mainly by the commercial availability of large amounts of kraft lignin and hydrolysis lignin in kraft pulp mills and cellulosic ethanol plants, there is a pressing need to valorize lignin for high‐value chemical and material products for better overall profitability for the plants, and for the emerging bioeconomy. To this end, we have developed, over 10 years and in several publications, an engineering approach to lignin valorization. This perspective paper provides an overview of this process and concretizes the research achieved in support of lignin valorization. In the method presented, lignin is first de‐polymerized into de‐polymerized lignin (DL) at a high yield and with a tunable Mw (weight average molecular weight). The DL is then utilized as a mixture (no separation needed) to substitute directly petroleum‐based phenol (up to 75% substitution), polyols (up to 50% substitution), and bis‐phenol A (100 substitution) in preparation of bio‐based phenolic resins, polyurethane foams, and epoxy resins. The DL products were also used to replace petroleum‐based antioxidants resulting in enhanced thermo‐oxidative and thermal stability of polyethylene in the synthesis of bio‐based resins / plastic composites. This approach has demonstrated both technical and economic feasibility, generating a payback period of approximately 3 years for a commercial capacity of 40 000 t/y. Thus, Lignin valorization beyond energy use can be profitable, and the old proverb may prove wrong. Lignin's time might have finally come! © 2020 Society of Industrial Chemistry and John Wiley & Sons Ltd