β-Zeolite Assisted Lignin-First Fractionation in a Flow-Through Reactor

<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>

β-Zeolite Assisted Lignin-First Fractionation in a Flow-Through Reactor

<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>

β-Zeolite Assisted Lignin-First Fractionation in a Flow-Through Reactor

<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>

Polyamides containing a biorenewable aromatic monomer based on coumalate esters: from synthesis to evaluation of the thermal and mechanical properties

A new biobased alternative for terephthalic acid (TPA) in (semi-)aromatic polyamides is proposed, namely 4-carboxybenzene propionic acid (4CBPA).

Performance of three delignifying pretreatments on hardwoods: hydrolysis yields, comprehensive mass balances, and lignin properties

Background In this work, three pretreatments under investigation at the DOE Bioenergy Research Centers (BRCs) were subjected to a side-by-side comparison to assess their performance on model bioenergy hardwoods (a eucalyptus and a hybrid poplar). These include co-solvent-enhanced lignocellulosic fractionation (CELF), pretreatment with an ionic liquid using potentially biomass-derived components (cholinium lysinate or [Ch][Lys]), and two-stage Cu-catalyzed alkaline hydrogen peroxide pretreatment (Cu-AHP). For each of the feedstocks, the pretreatments were assessed for their impact on lignin and xylan solubilization and enzymatic hydrolysis yields as a function of enzyme loading. Lignins recovered from the pretreatments were characterized for polysaccharide content, molar mass distributions, β-aryl ether content, and response to depolymerization by thioacidolysis. Results All three pretreatments resulted in significant solubilization of lignin and xylan, with the CELF pretreatment solubilizing the majority of both biopolymer categories. Enzymatic hydrolysis yields were shown to exhibit a strong, positive correlation with the lignin solubilized for the low enzyme loadings. The pretreatment-derived solubles in the [Ch][Lys]-pretreated biomass were presumed to contribute to inhibition of enzymatic hydrolysis in the eucalyptus as a substantial fraction of the pretreatment liquor was carried forward into hydrolysis for this pretreatment. The pretreatment-solubilized lignins exhibited significant differences in polysaccharide content, molar mass distributions, aromatic monomer yield by thioacidolysis, and β-aryl ether content. Key trends include a substantially higher polysaccharide content in the lignins recovered from the [Ch][Lys] pretreatment and high β-aryl ether contents and aromatic monomer yields from the Cu-AHP pretreatment. For all lignins, the 13C NMR-determined β-aryl ether content was shown to be correlated with the monomer yield with a second-order functionality. Conclusions Overall, it was demonstrated that the three pretreatments highlighted in this study demonstrated uniquely different functionalities in reducing biomass recalcitrance and achieving higher enzymatic hydrolysis yields for the hybrid poplar while yielding a lignin-rich stream that may be suitable for valorization. Furthermore, modification of lignin during pretreatment, particularly cleavage of β-aryl ether bonds, is shown to be detrimental to subsequent depolymerization.