The valorization of lignin, one of the main constituents of lignocellulosic biomass, is essential for an economically feasible biorefinery. In the present work, a hydrogen-free one step catalytic fractionation of woody biomass using commercial -zeolite as catalyst in a flow-through reactor was carried out, leading to a maximum aromatic monomer yield of 20.5 wt.%. Birch, spruce and walnut shells were compared as lignocellulosic feedstocks. -zeolite acts as a bifunctional catalyst, which prevents lignin repolymerization due to its size-selective properties and also cleaves -O-4 lignin intralinkage.Crucial to optimizing system operation, a rate limiting step analysis using different reactor configurations revealed a mixed regime where the rates of both solvolytic delignification and zeolite-catalyzed depolymerization/dehydration affect the net rate of aromatic monomer production. Oxalic acid co-feeding was found to enhance monomer production at moderate concentrations by improving solvolysis, while it caused structural changes to the zeolite and led to lower monomer yields at higher concentrations. Zeolite stability was assessed through catalyst recycling and characterization using NH3-TPD, XRD, N2 physisorption and TGA. Main catalyst deactivation mechanisms were found to be coking and leaching, leading to widening of the pores and decrease of zeolite acidity, respectively.

<p>Lignin is one of the main constituents of lignocellulosic biomass, whose valorization is essential for an economically feasible biorefinery process scheme. In the present work, a hydrogen-free one step catalytic fractionation of woody biomass using commercial b-zeolite as catalyst in a flow-through reactor was carried out, leading to a maximum aromatic monomer yield of 20.5 wt.%. Birch, spruce and walnut shells were used and compared as lignocellulosic feedstocks. Relevant insights in the reaction mechanism were obtained through 2D HSQC NMR analysis, revealing that b-O-4 cleavage is catalyzed by the zeolite. To optimize system operation, a rate limiting step analysis was performed by using different reactor configurations. It was found that the system operated in a mixed regime where the rates of both solvolytic delignification and zeolite-based depolymerization/dehydration affect the net rate of aromatic monomer production. Oxalic acid addition was found to enhance monomer production at moderate concentrations by improving solvolysis; however, it caused structural changes to the zeolite leading to lower monomer yields at higher concentrations. Zeolite stability was assessed through catalyst recycling and characterization using NH₃-TPD, XRD, N₂ physisorption and TGA. Main catalyst deactivation mechanisms were found to be coking and leaching, respectively leading to larger pore size and lower concentration of acid sites.</p>

<p>Lignin is one of the main constituents of lignocellulosic biomass, whose valorization is essential for an economically feasible biorefinery process scheme[1]. In the present work, a hydrogen-free one step catalytic fractionation of woody biomass using commercial b-zeolite as catalyst in a flow-through reactor was carried out, leading to a maximum aromatic monomer yield of 20.5 wt.%. Birch, spruce and walnut shells were used and compared as lignocellulosic feedstocks. Relevant insights in the reaction mechanism were obtained through 2D HSQC NMR analysis, revealing that b-O-4 cleavage is catalyzed by the zeolite. To optimize system operation, a rate limiting step analysis was performed by using different reactor configurations. It was found that the system operated in a mixed regime where the rates of both solvolytic delignification and zeolite-based depolymerization/dehydration affect the net rate of aromatic monomer production. Oxalic acid addition was found to enhance monomer production at moderate concentrations by improving solvolysis; however, it caused structural changes to the zeolite leading to lower monomer yields at higher concentrations. Zeolite stability was assessed through catalyst recycling and characterization using NH₃-TPD, XRD, N₂ physisorption and TGA. Main catalyst deactivation mechanisms were found to be coking and leaching, respectively leading to larger pore size and lower concentration of acid sites.</p>

The Cover Feature shows lignin‐first fractionation in a flow‐through reactor assisted by β‐zeolite. More information can be found in the Full Paper by A. Kramarenko et al.

<p>Lignin is one of the main constituents of lignocellulosic biomass, whose valorization is essential for an economically feasible biorefinery process scheme[1]. In the present work, a hydrogen-free one step catalytic fractionation of woody biomass using commercial b-zeolite as catalyst in a flow-through reactor was carried out, leading to a maximum aromatic monomer yield of 20.5 wt.%. Birch, spruce and walnut shells were used and compared as lignocellulosic feedstocks. Relevant insights in the reaction mechanism were obtained through 2D HSQC NMR analysis, revealing that b-O-4 cleavage is catalyzed by the zeolite. To optimize system operation, a rate limiting step analysis was performed by using different reactor configurations. It was found that the system operated in a mixed regime where the rates of both solvolytic delignification and zeolite-based depolymerization/dehydration affect the net rate of aromatic monomer production. Oxalic acid addition was found to enhance monomer production at moderate concentrations by improving solvolysis; however, it caused structural changes to the zeolite leading to lower monomer yields at higher concentrations. Zeolite stability was assessed through catalyst recycling and characterization using NH₃-TPD, XRD, N₂ physisorption and TGA. Main catalyst deactivation mechanisms were found to be coking and leaching, respectively leading to larger pore size and lower concentration of acid sites.</p>