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

Graphitization Behavior of Loblolly Pine Wood Investigated by <i>in Situ</i> High Temperature X‑ray Diffraction

Graphitization is a complex process involving chemical and morphological changes, although the detailed mechanism for different starting materials is not well understood. In this work, <i>in situ</i> high temperature X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to examine the phase transition occurring between 1000 and 1500 °C in loblolly pine wood-derived carbon materials. Electron energy loss spectroscopy (EELS) was also used to study these wood-derived carbon materials. XRD data showed the disappearance of a disordered carbon phase between 1300 and 1400 °C, followed by the formation of a crystalline graphitic phase between 1400 and 1500 °C. Lattice parameters and the crystal structure of the loblolly pine wood-derived graphite were systematically calculated from the empirical data. The presence of a large endothermic peak at 1500 °C in the DSC thermogram supported this observation. Selected area electron diffraction patterns showed the growth of graphitic crystallites after heat treatment. EELS spectra also supported the presence of a well-developed graphite structure

Toward Understanding of Bio-Oil Aging: Accelerated Aging of Bio-Oil Fractions

Pyrolysis bio-oil from biomass is a promising intermediate for producing transportation fuels and platform chemicals. However, its instability, often called aging, has been identified as a critical hurdle that prevents bio-oil from being commercialized. The objective of this research is to explore the bio-oil aging mechanism by an accelerated aging test of fractionated bio-oil produced from loblolly pine. When water soluble (WS), ether insoluble (EIS), and pyrolytic lignin (PL) fractions were aged separately, the increased molecular weight (Mw) was observed with increasing aging temperature and the presence of acids. WS and EIS fractions had high Mw brown solids formed after aging. Adjusting the pH of WS and EIS fractions from 2.5 to 7.0 significantly reduced the tendency of a Mw increase. Similar Mw rise was also observed on a PL fraction with an elevated temperature and acid addition. Formaldehyde was found to react with the PL fraction in the presence of any acid catalysts tested, i.e., 8-fold Mw increase in acetic acid environment, while other bio-oil aldehydes did not significantly promote lignin condensation. To better understand bio-oil stability, a potential bio-oil aging pattern was proposed, suggesting that bio-oil can be aged within or between its fractions

Interfacial Properties of Lignin-Based Electrospun Nanofibers and Films Reinforced with Cellulose Nanocrystals

Sub-100 nm resolution local thermal analysis, X-ray photoelectron spectroscopy (XPS), and water contact angle (WCA) measurements were used to relate surface polymer distribution with the composition of electrospun fiber mats and spin coated films obtained from aqueous dispersions of lignin, polyvinyl alcohol (PVA), and cellulose nanocrystal (CNC). Defect-free lignin/PVA fibers were produced with radii which were observed to increase with lignin concentration and with the addition of CNCs. XPS and WCA results indicate a nonlinear relationship between the surface and the bulk compositions. A threshold around 50 wt % bulk composition was identified in which extensive partitioning of PVA and lignin components occurred on the surface below and above this value. In 75:25 wt % lignin/PVA solvent cast films, phase separated domains were observed. Using nanoscale thermal analyses, the continuous phase was determined to be lignin-rich and the discontinuous phase had a lignin/PVA dispersion. Importantly, the size of the phase separated domains was reduced by the addition of CNCs. When electrospun fiber surfaces were lignin-rich, the addition of CNCs affected their surfaces. In contrast, no surface effects were observed with the addition of CNCs in PVA-rich fibers. Overall, we highlight the importance of molecular interactions and phase separation on the surface properties of fibers from lignin as an abundant raw material for the fabrication of new functional materials

Effects of Plant Cell Wall Matrix Polysaccharides on Bacterial Cellulose Structure Studied with Vibrational Sum Frequency Generation Spectroscopy and X‑ray Diffraction

The crystallinity, allomorph content, and mesoscale ordering of cellulose produced by Gluconacetobacter xylinus cultured with different plant cell wall matrix polysaccharides were studied with vibrational sum frequency generation (SFG) spectroscopy and X-ray diffraction (XRD). Crystallinity and ordering were assessed as the intensity of SFG signals in the CH/CH₂ stretch vibration region (and confirmed by XRD), while Iα content was assessed by the relative intensity of the OH stretch vibration at 3240 cm^–1. A key finding is that the presence of xyloglucan in the culture medium greatly reduced Iα allomorph content but with a relatively small effect on cellulose crystallinity, whereas xylan resulted in a larger decrease in crystallinity with a relatively small decrease in the Iα fraction. Arabinoxylan and various pectins had much weaker effects on cellulose structure as assessed by SFG and XRD. Homogalacturonan with calcium ion reduced the SFG signal, evidently by changing the ordering of cellulose microfibrils. We propose that the distinct effects of matrix polysaccharides on cellulose crystal structure result, at least in part, from selective interactions of the backbone and side chains of matrix polysaccharides with cellulose chains during the formation of the microfibril

Thermal and Storage Stability of Bio-Oil from Pyrolysis of Torrefied Wood

The objective of this paper is to investigate the biomass torrefaction effect on bio-oil stability by comparing the physicochemical and compositional properties of aged bio-oils. Two aging methods, accelerated aging (held at 80 °C for 24 h) and long-term natural aging (12-month storage at 25 °C), were employed to produce aged bio-oils for such comparison. The results indicate that bio-oils made from heat-treated wood had similar aging behavior in terms of increase of water content, acid content, molecular weight, and viscosity. The increase rate, however, was found to be different and dependent on the aging method. The accelerated method found parallel water and total acidity number (TAN) increments between raw and torrefaction bio-oils, while the natural aging method found torrefaction bio-oils, especially those made from heavily treated wood, had much slower water and acid accumulation than that of raw bio-oil. As a negative effect, both methods identified the viscosity of torrefaction bio-oils increased more significantly than that of raw bio-oil, while their molecular weights were unexpectedly lower. The correlation study showed that bio-oil viscosity is more tied to the content of bio-oil–water insoluble fraction rather than its average molecular weight. In addition, the characterization of aged bio-oils using NMR, GC/MS, and solvent fractionation indicated that torrefaction bio-oils had less compositional alternation after accelerated aging than the raw bio-oil. Also, they were more stable during the first 6 months of storage at room temperature. During the long-term storage, the raw bio-oil completely phase-separated after 6 months. However, two distinct torrefaction bio-oils (LP-280T and LP-330T) had enhanced phase stability, as a stable uniform oil phase without gum formation can be maintained during the entire 12-month storage

Understanding the Impacts of Biomass Blending on the Uncertainty of Hydrolyzed Sugar Yield from a Stochastic Perspective

Feedstock price and availability are key challenges for biorefinery development. Biomass blending has been suggested as a route to overcome these limitations. However, the impacts of feedstock blending on the uncertainty in hydrolyzed sugar yields remain unclear. This study quantifies the uncertainties in the sugar yields from hydrolysis of the blends of corn stover, switchgrass, and grass clippings by considering both feedstock compositional variation and model uncertainty. The results indicate that feedstock blending reduces the uncertainties in sugar yields and delivers feedstock of more uniform quality. A 60/35/5 blend of corn stover, switchgrass, and grass clippings on average achieves a glucose yield of 32.6 g/100 g of biomass, which is comparable to those of corn stover (33.3 g/100 g) and switchgrass (32.9 g/100 g), but drastically higher than that of grass clippings (21.7 g/100 g). This same blend also achieves the lowest variance in glucose yield (2.9 g/100 g) compared to corn stover (3.1 g/100 g), switchgrass (3.3 g/100 g), and grass clippings (5.6 g/100 g). A further investigation on the breakdown of the variability of the hydrolyzed sugar yields reveals that the reduction in the variability of sugar yields for blended feedstocks is achieved by reduced feedstock compositional variation. Based on these results, the optimization of blending ratios is performed with respect to three objectives: (1) to maximize the probability of meeting the sugar yields target, (2) to maximize the expected sugar yields, and (3) to maximize sugar yields per unit feedstock expense, while satisfying constraints of feedstock availability and price. The maximized probability of meeting the sugar yield target, expected sugar yield, and glucose yield per unit feedstock expense are 91.33%, 32.66 g of sugar/100 g of biomass, and 40.83 g/$, respectively. The optimization method developed in this study is readily applied to other combinations of feedstocks, biofuel production processes, and constraints

Understanding the Impacts of Biomass Blending on the Uncertainty of Hydrolyzed Sugar Yield from a Stochastic Perspective

Feedstock price and availability are key challenges for biorefinery development. Biomass blending has been suggested as a route to overcome these limitations. However, the impacts of feedstock blending on the uncertainty in hydrolyzed sugar yields remain unclear. This study quantifies the uncertainties in the sugar yields from hydrolysis of the blends of corn stover, switchgrass, and grass clippings by considering both feedstock compositional variation and model uncertainty. The results indicate that feedstock blending reduces the uncertainties in sugar yields and delivers feedstock of more uniform quality. A 60/35/5 blend of corn stover, switchgrass, and grass clippings on average achieves a glucose yield of 32.6 g/100 g of biomass, which is comparable to those of corn stover (33.3 g/100 g) and switchgrass (32.9 g/100 g), but drastically higher than that of grass clippings (21.7 g/100 g). This same blend also achieves the lowest variance in glucose yield (2.9 g/100 g) compared to corn stover (3.1 g/100 g), switchgrass (3.3 g/100 g), and grass clippings (5.6 g/100 g). A further investigation on the breakdown of the variability of the hydrolyzed sugar yields reveals that the reduction in the variability of sugar yields for blended feedstocks is achieved by reduced feedstock compositional variation. Based on these results, the optimization of blending ratios is performed with respect to three objectives: (1) to maximize the probability of meeting the sugar yields target, (2) to maximize the expected sugar yields, and (3) to maximize sugar yields per unit feedstock expense, while satisfying constraints of feedstock availability and price. The maximized probability of meeting the sugar yield target, expected sugar yield, and glucose yield per unit feedstock expense are 91.33%, 32.66 g of sugar/100 g of biomass, and 40.83 g/$, respectively. The optimization method developed in this study is readily applied to other combinations of feedstocks, biofuel production processes, and constraints

Green Needle Coke Production from Pyrolysis Biocrude toward Bio-based Anode Material Manufacture: Biochar Fines Addition Effect as “Physical Template” on the Crystalline Order

A new method for producing green needle coke (GNC) is developed by replacing the “heavy fraction” of petroleum pitch delayed coking with fast pyrolysis biocrude. A series of alternative biocrude distillation, carbonization, and calcination conditions were investigated to determine the influence of these processing parameters onto the crystalline structure of the resulting graphitized material. For the first time, the addition of biochar fines was found to serve as a “physical template” to increase the graphitic nature of the final product. During the initial biocrude carbonization (350–450 °C), volatile compounds are released, and aromatics in pyrolysis biocrude experience condensation, resulting in GNC solids with carbon contents above 95 wt % and some early lamellar structure. In the second stage of the thermal process (25–1500 °C), there are additional thermal decomposition reactions with an increase in the aromatic nature of the graphitized solid. It was found that systematic addition of biochar fines induces a nucleating effect during the GNC development. Thermogravimetric analysis suggests that biochar fines promote polycondensation reactions by modifying the biopitch structure and molecular weight, while elemental analysis (CHN) shows a reduction in both H/C and O/C ratios which are consistent with the increase in aromaticity and removal of oxygenated compounds as thermal treatment evolves. The effects of different bio-based pitch materials (after distillation) and GNC intermediates were evaluated by pyrolysis-gas chromatography mass spectrometry and Fourier transform infrared, displaying slight changes on product yields and quality. X-ray diffraction patterns taken after graphitization evidence an increase in the graphitic order with the addition of biochar fines. Transmittance electron microscopy depicts an improvement on graphitic morphology as biochar fine content increases. The use of biochar fines showed a significant increase in graphitic ordering at addition levels above 0.01 wt %. These results show that thermally treated biocrude/biochar fine systems can produce graphitic structures (hard carbon-like) that might be suitable for the manufacture of sodium-ion batteries