Hybrid Catalytic Biorefining of Hardwood Biomass to Methylated Furans and Depolymerized Technical Lignin

Abstract

A robust method is needed to achieve high yield all-catalytic conversion of recalcitrant lignocellulosic biomass to transportation fuels while maximizing carbon utilization from raw substrates. To accomplish this, we developed an integrated strategy that combines homogeneous and heterogeneous reactions with a treatment-extraction step to coproduce 2-methylfuran (MF) and 2,5-dimethylfuran (DMF) directly from hardwood poplar while maintaining high catalyst activity. In the first step, poplar wood chips were treated with dilute FeCl 3 in THF−water at subpyrolytic temperature to yield 93.5% furfural (FF) from xylan and 66.0% 5-hydroxymethylfurfural (HMF) from glucan. Concurrently, a highly pure lignin powder was obtained from the liquor by precipitation upon room temperature vacuum recovery of THF from the water. Afterward, FF and HMF were extracted from water into an organic phase consisting of toluene and 1,4-dioxane treated with Ca(OH) 2. A second hydrodeoxygenation reaction using Cu−Ni/TiO 2 catalyst yielded 87.8% MF from FF and 85.6% DMF from HMF. Characterization of the lignin product showed its molecular weight to be reduced by an order of magnitude from its native state as well as complete removal of its native β-aryl ether linkages without hydrogen input or further heterogeneous catalytic processing. A 60% cumulative yield of MF, DMF, and lignin products from the available carbon (xylan+glucan+lignin) in poplar was achieved, rivaling more mature cellulosic ethanol strategies.

Heterogeneous Catalyst Design Principles for the Conversion of Lignin into High‐Value Commodity Fuels and Chemicals

“…The extracted lignin contains a minimal amount of ashes and sugars for more effective catalytic upgrading, serving as the primary lignin feedstock to many of the catalytic systems mentioned herein. Cosolvent systems, such as ethanol–water, methanol–water, acetone–water, formic acid–water, THF–water, and gamma‐valerolactone (GVL)–water, have been shown to produce high‐quality lignin feedstocks. The lignin is precipitated out and has a higher purity and less structural changes than that of acid and base pretreated lignin .…”

“…At a high level, catalytic processing can be categorized as either homo‐ or heterogeneous that can be differentiated by the use of catalysts that are either soluble or insoluble in the liquid medium, respectively, during the intended reaction. Both types are useful for processing biomass and biomass‐derived intermediates and a combined strategy is often proposed to take advantage of the merits of both . Homogeneous catalysis for biomass upgrading primarily addresses the challenges of the direct processing of raw biomass feedstocks to drive sufficient biomass deconstruction by solubilization, hydrolysis, and dehydration to liquid chemical intermediates, such as sugars, furfurals, oxo acids, polyols, and depolymerized technical lignins .…”

“…However, homogeneous biomass reactions often produce a limited scope of water‐soluble intermediates that necessitate subsequent separation steps to recover valuable reactive chemical intermediates, while separating them from the catalytic component and contaminates, such as mineral ash, chlorine, and acids. A recent integrated approach of a homogeneous reaction in tandem with a heterogeneous process has achieved an impressive 60 % total carbon utilization of biomass to fungible fuels and technical‐grade lignin . Heterogeneous catalysts can be manipulated to extend chemistries not seen in homogeneous catalysis, although heterogeneous catalysts have issues of their own, when it comes to the surface‐active sites of the catalyst interacting with the lignin polymeric structure.…”

Characterization of fractional cuts of co-solvent enhanced lignocellulosic fractionation lignin isolated by sequential precipitation

“…Baseline Populus (trichocarpa x deltoides) was harvested from Oak Ridge National Laboratory (ORNL) and shipped to National Renewable Energy Laboratory (NREL) for drying, debarking, and size-reduction. Extractives were removed by an ethanol/toluene Soxhlet extraction, and the composition of the poplar was measured to be ∼45% glucan, ∼15% xylan, and ∼22% Klason lignin via a NREL procedure (Seemala et al, 2018;Sluiter et al, 2008). Hydrated ferric chloride was purchased from Sigma Aldrich (St. Louis, MO).…”

“…During CELF pretreatment, 85%-90% of the lignin can be solubilized into the co-solvent mixture, and an ash-free and sugar-free product known as CELF lignin can be obtained by precipitation after boiling off the THF (Cai et al, 2014(Cai et al, , 2013. Recent studies have found that CELF lignin drastically reduces molecular weight from native lignin while minimizing competing cross-condensation reactions Thus, CELF process could serve as a unique tool to produce highly fractionated lignin (Meng et al, 2018;Seemala et al, 2018).…”