• Energy Research

Lignin is an aromatic polymer that constitutes up to 30 wt% of woody biomass and is considered the largest source of renewable aromatics. Valorization of the lignin stream is pivotal for making biorefining sustainable. Monomeric units in lignin are bound via C-O and C-C bonds. The majority of existing methods for the production of valuable compounds from lignin are based on the depolymerization of lignin via cleavage of relatively labile C-O bonds within lignin structure, which leads to yields of only 36-40 wt%. The remaining fraction (60 wt%) is a complex mixture of high-molecular-weight lignin, generally left unvalorized. Here we present a method to produce additional valuable monomers from the high-molecular-weight lignin fraction through oxidative C-C bond cleavage. This oxidation reaction proceeds with a high selectivity to give 2,6-dimethoxybenzoquinone (DMBQ) from high-molecular-weight lignin in 18 wt% yield, thus increasing the yield of monomers by 32%. This is an important step to make biorefining competitive with petroleum-based refineries.

La primera biorrefinación con lignina del álamo nórdico para producir fibras de celulosa podría desplazar la producción de algodón en tierras agrícolas Al cruzar Populus trichocarpa 3 P. trichocarpa de una población distante, se obtuvieron álamos híbridos que pueden crecer rápidamente en tierras marginales en climas del norte. Estos híbridos pueden transformarse mediante fraccionamiento catalítico reductor para producir una fibra textil deslignificada que puede ser un sustituto del algodón, así como un biocombustible alimentado con lignina en el rango de gasolina-aviación-diesel. La sostenibilidad de esta cadena de valor fue evaluada por LCA y mostró beneficios sustanciales en términos de uso de agua en comparación con la producción de algodón. Le bioraffinage en lignine du peuplier nordique pour produire des fibres de cellulose pourrait déplacer la production de coton sur les terres agricoles En croisant Populus trichocarpa 3 P. trichocarpa d'une population éloignée, des peupliers hybrides ont été obtenus qui peuvent croître rapidement sur des terres marginales dans les climats nordiques. Ces hybrides peuvent être transformés par fractionnement catalytique réducteur pour donner une fibre textile délignifiée qui peut remplacer le coton ainsi qu'un biocarburant ligninérisé dans la gamme essence-aviation-diesel. La durabilité de cette chaîne de valeur a été évaluée par LCA et a montré des avantages substantiels en termes d'utilisation de l'eau par rapport à la production de coton. Lignin-first biorefining of Nordic poplar to produce cellulose fibers could displace cotton production on agricultural lands By crossing Populus trichocarpa 3 P. trichocarpa from a distant population, hybrid poplar trees were obtained that can grow rapidly on marginal lands in northern climates.These hybrids can be transformed by reductive catalytic fractionation to yield a delignified textile fiber that can be a substitute for cotton as well as a ligninderived biofuel in the gasoline-aviation-diesel range.The sustainability of this value chain was evaluated by LCA and showed substantial benefits in terms of water use compared with cotton production. يمكن للتكرير الحيوي الأول لليجنين للحور الشمالي لإنتاج ألياف السليلوز أن يحل محل إنتاج القطن في الأراضي الزراعية من خلال عبور Populus trichocarpa 3 P. trichocarpa من مجموعة سكانية بعيدة، تم الحصول على أشجار الحور الهجينة التي يمكن أن تنمو بسرعة على الأراضي الهامشية في المناخات الشمالية. يمكن تحويل هذه الهجينة عن طريق التجزئة التحفيزية المختزلة لإنتاج ألياف نسيج منزوعة الكرامة يمكن أن تكون بديلاً عن القطن بالإضافة إلى وقود حيوي خفيف في نطاق البنزين والطيران والديزل. تم تقييم استدامة سلسلة القيمة هذه من قبل LCA وأظهرت فوائد كبيرة من حيث استخدام المياه مقارنة بإنتاج القطن.

AbstractOrganosolv pulping releases reactive monomers from both lignin and hemicellulose by the cleavage of weak C−O bonds. These monomers recombine to form undesired polymers through the formation of recalcitrant C−C bonds. Different strategies have been developed to prevent this process by stabilizing the reactive monomers (i.e., lignin‐first approaches). To date, all reported approaches rely on the addition of capping agents or metal‐catalyzed stabilization reactions, which usually require high pressures of hydrogen gas. Herein, a metal‐ and additive‐free approach is reported that uses zeolites as acid catalysts to convert the reactive monomers into more stable derivatives under organosolv pulping conditions. Experiments with model lignin compounds showed that the recondensation of aldehydes and allylic alcohols produced by the cleavage of β‐O‐4′ bonds was efficiently inhibited by the use of protonic β zeolite. By applying a zeolite with a preferred pore size, the bimolecular reactions of reactive monomers were effectively inhibited, resulting in stable and valuable monophenolics. The developed methodology was further extended to birch wood to yield monophenolic compounds and value‐added products from carbohydrates.

Analysis of a promising lignin-first biorefining technique, reductive catalytic fractionation, provides useful metrics for cost and sustainability to guide researchers toward critical areas for improvement.

A reductive fractionation process for the valorization of Quercus suber bark toward hydrocarbons in gasoline and diesel ranges and optionally 4-ethylguaiacol has been developed. The procedure involves three steps: (1) tandem hydrogen-free Pd/C-catalyzed transfer hydrogenolysis of lignin where the carbohydrates serve as an inherent hydrogen donor under slightly alkaline conditions to also facilitate the depolymerization of suberin, (2) optional distillation, to isolate the 4-ethylguaiacol, (3) hydrodeoxygenation of the mixture from the first step by a Pt-MoO3/TiO2 catalyst generated hydrocarbons in gasoline and diesel ranges. The yield of 4-ethylguaiacol (90% purity) is 2.6% of dry bark weight (12% of acid insoluble lignin), and yield of hydrocarbon bio-oil is 42% of dry bark weight. This corresponds to a theoretical maximum yield of 77% for lignin and suberin. The carbon yield of the obtained bio-oil is thereby 64% from the total initial bark.

With these guidelines, we aim to unite the lignin-first biorefining research field around best practices for performing or reporting feedstock analysis, reactor design, catalyst performance, and product yields.