Soluble Lignin Recovered from Biorefinery Pretreatment Hydrolyzate Characterized by Lignin–Carbohydrate Complexes

The lignin rendered soluble by lignocellulosic biorefinery pretreatment remains insufficiently understood along the lines of molecular properties and chemical composition. To procure a representative soluble lignin preparation, an aromatic-selective adsorptive resin was utilized. Approximately 90% of soluble lignin could be recovered from autohydrolysis pretreatment hydrolyzate (autohydrolyzate) produced from a hardwood and a nonwood biomass. Adsorbate compositional characterization revealed a befuddling magnitude of carbohydrate in selectively isolated lignin adsorbates. Quantitative structural analysis of the lignin by NMR suggested lignin–carbohydrate complexes (LCCs) as the cause behind the pronounced carbohydrate contents. Analyzed spectra revealed both hardwood and nonwood soluble lignin features of ∼10 total LCC per 100 aromatic rings, with each lignin bearing unique LCC profiles. In addition, native structures remained in large quantities. The improved understanding of hydrolyzate-soluble lignin granted from this work will aid biorefinery development by improving discourse around a biorefinery lignin source

Catalytic Conversion of Biomass Hydrolysate into 5‑Hydroxymethylfurfural

Biomass hydrolysate, rich in glucose, was used to produce an important platform chemical, 5-hydroxymethylfurfural (HMF). By separating the solid biomass from solution after autohydrolysis, most of the inhibitors were removed from hydrolysate. Biphasic system, which prevents the HMF degradation, was optimized with HCl and AlCl₃ catalysts. The yield of HMF conversion using biomass hydrolyzate under the optimized reaction conditions is comparable to the yield using pure glucose as a feedstock. This lab-generated HMF was purified via activated charcoal and oxidized to high value-added chemical, 2,5-furandicarboxylic acid (FDCA). The final FDCA yield of 65% was achieved. The results suggest that, with the separation of nonsugar components such as dissolved lignin and sugar degradation products, biomass hydrolysate is a promising source for HMF and FDCA production

Phenolation to Improve Lignin Reactivity toward Thermosets Application

Phenolation can be used to improve the reactivity and decrease the molecular weight of lignin, thereby making it more useful for various applications. We report an effective phenolation process with only a catalytic amount of sulfuric acid and using phenol as solvent. The optimum phenolation conditions for pine kraft lignin and sweetgum biorefinery lignin were determined to be lignin/phenol (L/P, wt/wt) of 3/5, 5% acid charge at 90 °C for 2 h and L/P of 2/5, 5% acid charge at 110 °C for 2 h, respectively. Phenolation resulted in introducing 30 wt % of phenol onto pine kraft lignin and 60 wt % of phenol onto sweetgum biorefinery lignin and significantly decreasing in the molecular weight of lignin. Phenol was incorporated onto both the side chains and aromatic nuclei of lignin. All lignin substructures of β-O-4′, β-5′/α-O-4′, β–β′, α-carbonyl, etc. were reacted, resulting in a significant decrease in aliphatic hydroxyl groups and increase in the phenolic hydroxyl groups. The comprehensive characterization revealed that most of the ethers linkages were cleaved during phenolation. The β-elimination of the γ-hydroxymethyl group as formaldehyde was the main reaction of side chains. The released formaldehyde reacted with phenol and lignin to form diphenylmethanes. Plausible mechanisms for lignin phenolation are also discussed

Field-Grown Transgenic Hybrid Poplar with Modified Lignin Biosynthesis to Improve Enzymatic Saccharification Efficiency

Hybrid poplars (<i>Populus nigra</i> L. × <i>Populus maximowiczii</i> A.) were genetically modified through antisense insertion of the 4-coumarate:coenzyme A ligase (4CL) gene. Compositional changes in response to this genetic change were measured in the field after 2 and 3 years of growth. The stem samples were treated with either green liquor or dilute acid pretreatments, representing alkaline and acid pretreatments. The enzymatic saccharification of the untreated and pretreated transgenic poplars were evaluated. After transgenic species were transplanted into the environment, they showed reduced recalcitrance to chemicals (i.e., pretreatments) and enzymes despite their lignin content and S/V ratio being comparable to those of the wild types. Compared to the field-grown poplars, the sugar yield increased up to 103% for untreated transgenic samples and increased 22% for acid- and green liquor-pretreated transgenic samples. This shows that field-grown transgenic hybrid poplars with modified lignin biosynthesis have improved enzymatic saccharification efficiency (sugar recovery and yield)