Reductive lignocellulose fractionation into soluble lignin-derived phenolic monomers and dimers and processable carbohydrate pulps

Abstract

A catalytic lignocellulose biorefinery process is presented, valorizing both polysaccharide and lignin components into a handful of chemicals. To that end, birch sawdust is efficiently delignified through simultaneous solvolysis and catalytic hydrogenolysis in the presence of a Ru on carbon catalyst (Ru/C) in methanol under a H-2 atmosphere at elevated temperature, resulting in a carbohydrate pulp and a lignin oil. The lignin oil yields above 50% of phenolic monomers (mainly 4-n-propylguaiacol and 4-n-propylsyringol) and about 20% of a set of phenolic dimers, relative to the original lignin content, next to phenolic oligomers. The structural features of the lignin monomers, dimers and oligomers were identified by a combination of GC/MS, GPC and 2D HSQC NMR techniques, showing interesting functionalities for forthcoming polymer applications. The effect of several key parameters like temperature, reaction time, wood particle size, reactor loading, catalyst reusability and the influence of solvent and gas were examined in view of the phenolic product yield, the degree of delignification and the sugar retention as a first assessment of the techno-economic feasibility of this biorefinery process. The separated carbohydrate pulp contains up to 92% of the initial polysaccharides, with a nearly quantitative retention of cellulose. Pulp valorization was demonstrated by its chemocatalytic conversion to sugar polyols, showing the multiple use of Ru/C, initially applied in the hydrogenolysis process. Various lignocellulosic substrates, including genetically modified lines of Arabidopsis thaliana, were finally processed in the hydrogenolytic biorefinery, indicating lignocellulose rich in syringyl-type lignin, as found in hardwoods, as the ideal feedstock for the production of chemicals

Complete lignocellulose conversion with integrated catalyst recycling yielding valuable aromatics and fuels

“…To our surprise, at 180 °C, the small molecule fraction of the liquid phase contained predominantly one aromatic compound, dihydroconiferyl alcohol (1G), which could be isolated. Earlier studies using noble-metal catalysts and higher temperatures reported 2G as the main product in mixtures, and 1G was also seen before 16 . Remarkably, in our system 1G was obtained in excellent (> 90%) selectivity (Fig.…”

“…While these methods hold much promise for the selective production of aromatic monomers from the lignin fraction, they leave a significant portion of the renewable carbon equivalents unutilized and mixed with the catalyst. Thus, in these systems it is (mainly) the cellulose part that is tedious to valorize and catalyst recycling has been identified as a key challenge 4,16 .…”

“…This remains true despite impressive advances in the selective conversion of lignin model compounds 8,9 and depolymerization of organosolv lignin [10][11][12][13][14] . Recently, elegant research has focused on lignocellulose fractionation in the presence of a catalyst 4,[15][16][17] . While these methods hold much promise for the selective production of aromatic monomers from the lignin fraction, they leave a significant portion of the renewable carbon equivalents unutilized and mixed with the catalyst.…”

Mapping reactivities of aromatic models with a lignin disassembly catalyst. Steps toward controlling product selectivity

“…12 Effective utilization of lignin remains a major intellectual challenge [1][2][3] that is drawing increasing interest from the chemical community. [13][14][15][16][17][18][19][20] Our laboratories previously demonstrated the clean reductive disassembly of organosolv lignin to organic liquids without formation of intractable chars or tars. 21 This process is heterogeneously catalysed by a copper-doped porous metal oxide (Cu20PMO) that is prepared by calcining a 3 : 1 Mg 2+ : Al 3+ hydrotalcite in which 20% of the Mg 2+ had been replaced by Cu 2+ .…”

A Key Role for Apoplastic H2O2 in Norway Spruce Phenolic Metabolism

“…Lignin has a high economic impact, as it hinders the industrial processing of lignocellulosic biomass into pulp and fermentable sugars, leading to large economic costs to extract it from the biomass. On the other hand, lignin is increasingly considered as a potentially valuable product, and new applications and profit revenues for this biopolymer are being identified (Ragauskas et al, 2014;Van den Bosch et al, 2015). In Norway spruce (Picea abies), an economically important conifer in Europe, lignin is composed mainly of coniferyl alcohol giving rise to G units, with a small proportion of p-coumaryl alcohol-derived H units (Boerjan et al, 2003).…”