Ozone mediated depolymerization and solvolysis of technical lignins under ambient conditions in ethanol

Technical lignins are highly available and inexpensive feedstocks derived from current large scale biomass utilizing industries. Their valorization represents a bottleneck in the development of biorefineries, as the inherently complex lignin structure often suffers severe condensation during isolation, leading to their current application as low value fuel. Processes able to depolymerize technical lignins into value-added (intermediate) molecules are of great interest for the development of integrated, viable routes aiming at the full valorization of lignocellulosic biomass. Here, we report an effective ozone mediated depolymerization of four technical lignins (Indulin-AT Kraft, ball-milled Indulin-AT Kraft, Alcell organosolv and Fabiola organosolv) in ethanol under ambient conditions without the need for catalysts. 52–87 wt% of these nearly ethanol insoluble lignins was broken down into soluble fragments upon ozone exposure. The average molecular weight of the soluble fragments was shown to have decreased by 40–75% compared to the parent materials. A range of (di)carboxylic acids and (di)ethyl esters was identified, accounting for up to 40 wt% of the ozonated lignin oils. These products are the result of phenol ring-opening reactions as well as oxidative cleavage of unsaturated linking motifs followed by partial esterification. Reactivity varied substantially among the lignin feedstocks. For instance, lower particle sizes and higher degradation of the native lignin structure were shown to be beneficial for the effective action of the ozone. Our results show that a straightforward ozonation process under ambient conditions can depolymerize recalcitrant lignins into oxygenated fragments and low molecular weight products soluble in ethanol. These can potentially be used for the synthesis of high-value drop-in chemicals

Catalytic hydrotreatment of pyrolytic lignins from different sources to biobased chemicals:Identification of feed-product relations

The pyrolysis liquid biorefinery concept involves separation of pyrolysis liquids in various fractions followed by conversion of the fractions to value-added products. Pyrolytic lignins (PLs), the water-insoluble fractions of pyrolysis liquids, are heterogeneous, cross linked oligomers composed of substituted phenolics whose structure and physicochemical properties vary significantly depending on the biomass source. The catalytic hydrotreatment of six PLs from different biomass sources (pine, prunings, verge grass, miscanthus and sunflower seed peel) was investigated to determine the effect of different feedstocks on the final product composition and particularly the amount of alkylphenolics and aromatics, the latter being important building blocks for the chemical industry. Hydrotreatment was performed with Pd/C, 100 bar of hydrogen pressure and temperatures in the range of 350–435 °C, resulting in depolymerized product mixtures with monomer yields up to 39.1 wt% (based on PL intake). The molecular composition of the hydrotreated oils was shown to be a strong function of the PL feed and reaction conditions. Statistical analyses provided the identification of specific structural drivers on the formation of aromatics and phenolics, and a simple model able to accurately predict the yields of such monomers after catalytic hydrotreatment was obtained (R2 = 0.9944) and cross-validated (R2 = 0.9326). These feed-product relations will support future selections of PL feeds to obtain the highest amounts of valuable biobased chemicals

Density structure of Earth's lowermost mantle from Stoneley mode splitting observations

Advances in our understanding of Earth’s thermal evolution and the style of mantle convection rely on robust seismological constraints on lateral variations of density. The large-low-shear-wave velocity provinces (LLSVPs) atop the core–mantle boundary beneath Africa and the Pacific are the largest structures in the lower mantle, and hence severely affect the convective flow. Here, we show that anomalous splitting of Stoneley modes, a unique class of free oscillations that are perturbed primarily by velocity and density variations at the core–mantle boundary, is explained best when the overall density of the LLSVPs is lower than the surrounding mantle. The resolved density variations can be explained by the presence of post-perovskite, chemical heterogeneity or a combination of the two. Although we cannot rule out the presence of a ∼100-km-thick denser-than-average basal structure, our results support the hypothesis that LLSVPs signify large-scale mantle upwelling in two antipodal regions of the mantle

Pyrolytic lignin:A promising biorefinery feedstock for the production of fuels and valuable chemicals

Lignocellulosic biomass is a key feedstock for the sustainable production of biofuels, biobased chemicals and performance materials. Biomass can be efficiently converted into pyrolysis liquids (also known as bio-oils) by the well-established fast pyrolysis technology. Currently, there is significant interest in the application of fast pyrolysis technology as principle biomass conversion technology due to its feedstock flexibility, low cost and high energy conversion efficiency, with many emerging commercial enterprises being established around the globe. Upgrading of the bio-oils is a requisite, and is complicated by its complex and heterogeneous organic nature. Pyrolysis liquids may be further separated by a simple water fractionation, yielding an aqueous sugar-rich phase and a water-insoluble pyrolytic lignin (PL) fraction. This separation step allows the use of dedicated conversion strategies for each fraction, which can be highly advantageous due to their differences in composition and reactivity. For example, the sugar-rich fractions can be used for fermentation, while the phenolic-rich PL is a particularly promising feedstock for the production of a wide range of platform chemicals and energy-dense streams upon depolymerization. To aid the emerging use of PL, novel characterization techniques and valorization strategies are being explored. In this review, the fast pyrolysis process and PL characterization efforts are discussed in detail, followed by the state-of-the-art regarding PL processing using both oxidative and reductive (catalytic) strategies, as well as a combination thereof. Possible applications are discussed and recommendations for future research are provided

Valorization of humin type byproducts from pyrolytic sugar conversions to biobased chemicals

The pyrolytic sugar fraction, obtained by an aqueous extraction of pyrolysis oil, is an attractive source for sugar-derived platform chemicals. However, solids (humin) formation occurs to a significant extent during hydrolysis and subsequent acid-catalyzed conversion processes. In this study, we report investigations on possible conversion routes (pyrolysis, liquefaction) of such humin byproducts to biobased chemicals. Experiments were carried out with a model humin made from a representative technical pyrolytic sugar and the product was characterized by elemental analysis, GPC, TGA, HPLC, GC-MS, FT-IR and NMR. The obtained humin sample is soluble in organic solvents (dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), and isopropanol (IPA)), in contrast to typical more condensed humins from glucose and fructose, allowing characterization using NMR and GPC. All analyses reveal that the humins are oligomeric in nature (M-w of about 900 g/mol) and consist of sugar and furanic fragments linked with among others (substituted) aliphatic, ester units and, in addition, phenolic fragments with methoxy groups. The humins were used as a feed for catalytic pyrolysis and catalytic liquefaction experiments. Catalytic pyrolysis experiments (mg scale, programmable temperature vaporizer (PTV)-GC-MS, 550 degrees C) with HZSM-5 50 as the catalyst gave benzene-toluene-xylene-naphthalene-ethylbenzene mixtures (BTXNE) in 5.1 wt% yield based on humin intake. Liquefaction experiments (batch reactor, 350 degrees C, 4 h, isopropanol as both the solvent and hydrogen donor and Pt/CeO2 (4.43 wt% Pt) catalyst) resulted in 80 wt% conversion of the humin feed to a product oil with considerable amounts of phenolics and aromatics (ca. 24.7 % based on GC detectables in the humin oil). These findings imply that the techno-economic viability of pyrolysis oil biorefineries can be improved by converting humin type byproducts to high value, low molecular weight biobased chemicals

Efficient depolymerization of lignin to biobased chemicals using a two-step approach involving ozonation in a continuous flow microreactor followed by catalytic hydrotreatment

Lignin is a promising feedstock for the replacement of conventional carbon sources for the production of chemicals and fuels. In this paper, results are reported for the depolymerization of various residual lignins in the absence of a catalyst by utilizing ozone. Reactions were performed in a microreactor setup ensuring high gas-liquid mass transfer rates, a low inventory of ozone, and straightforward scale-up possibilities. The ozonation is demonstrated using a representative model compound (vanillin) and various lignins (pyrolytic and organosolv) dissolved in methanol (2.5 wt %). Experiments were performed under ambient conditions, at gas-liquid flow ratios ranging from 30 to 90 and short residence times on the order of 12-24 s. Analyses of the products after methanol removal revealed the presence of (di)carboxylic acids, methyl esters, and acetals. Extensive depolymerization was achieved (i.e., up to 30% for pyrolytic lignin and 70% for organosolv lignins). Furthermore, a two-step approach in which the ozonated lignin is further hydrotreated (350-400 degrees C, 100 bar H-2, 4 h, Pd/C as catalyst) showed a substantial increase in depolymerization efficiency, yielding a 2.5-fold increased monomer yield in the product oil compared to a hydrotreatment step only

Substituted anilides from chitin-based 3-acetamido-furfural

The synthesis of aromatic compounds from biomass-derived furans is a key strategy in the pursuit of a sustainable economy. Within this field, a Diels-Alder/aromatization cascade reaction with chitin-based furans is emerging as a powerful tool for the synthesis of nitrogen-containing aromatics. In this study we present the conversion of chitin-based 3-acetamido-furfural (3A5F) into an array of di- and tri-substituted anilides in good to high yields (62-90%) via a hydrazone mediated Diels-Alder/aromatization sequence. The addition of acetic anhydride expands the dienophile scope and improves yields. Moreover, replacing the typically used dimethyl hydrazone with its pyrrolidine analogue, shortens reaction times and further increases yields. The hydrazone auxiliary is readily converted into either an aldehyde or a nitrile group, thereby providing a plethora of functionalized anilides. The developed procedure was also applied to 3-acetamido-5-acetylfuran (3A5AF) to successfully prepare a phthalimide. </p

Biobased chemicals from the catalytic depolymerization of Kraft lignin using supported noble metal-based catalysts

Kraft lignin, a side-product of the paper industry, is considered an attractive feedstock for the production of biorenewable chemicals. However, its recalcitrant nature and sulfur content render catalytic conversions challenging. This study demonstrates the efficacy of noble metal-based catalysts for the production of a lignin oil enriched in alkylphenolic and aromatic compounds, by a catalytic hydrotreatment of Kraft lignin without the use of an external solvent. Eight commercially available catalysts were evaluated using four different metals (Ru, Pt, Pd, Rh) on two supports (activated carbon and Al2O3). The product oils were extensively analyzed by means of GPC, GCxGC-FID, GC-MS-FID, and elemental analysis. The catalysts were characterized by various techniques (N-2 physisorption, NH3-TPD, XRD and TEM) before and after reaction, and their physico-chemical properties were correlated with catalytic performance. Al2O3 as support gave better results than carbon as support in terms of lignin oil yield and composition, due to a combination of higher total acidity, mildly acidic sites and a mesoporous structure. The metallic phase also significantly affected product distribution. The best results were obtained using a Rh/Al2O3 catalyst, resulting in a lignin oil yield of 36.3 wt% on a lignin intake and a total monomer yield of 30.0 wt% on lignin intake including 15.3 wt% of alkylphenolic and 7.9 wt% of aromatic compounds, and with a sulfur content <0.01 wt%

Biobased Furanics:Kinetic Studies on the Acid Catalyzed Decomposition of 2-Hydroxyacetyl Furan in Water Using Bronsted Acid Catalysts

Biobased furanics like 5-hydroxymethylfurfural (5-1-IMF) are interesting platform chemicals for the synthesis of biofuel additives and polymer precursors. 5-HMF is typically prepared from C6 ketoses like fructose, psicose, sorbose and tagatose. A known byproduct is 2-hydroxyacetylfuran (2-HAF), particularly when using sorbose and psicose as the reactants. We here report an experimental and kinetic modeling study on the rate of decomposition of 2-HAF in a typical reaction medium for 5-HMF synthesis (water, Bronsted acid), with the incentive to gain insights in the stability of 2-HAF. A total of 12 experiments were performed (batch setup) in water with sulfuric acid as the catalyst (100-170 degrees C, C-H2SO4 ranging between 0.033 and 1.37 M and an initial 2-HAF concentration between 0.04 and 0.26 M). Analysis of the reaction mixtures showed a multitude of products, of which levulinic acid (LA) and formic acid (FA) were the most prominent (Y-max,Y-FA = 24 mol %, Y-max,Y-LA = 10 mol %) when using HCI. In contrast, both LA and FA were formed in minor amounts when using H2SO4 as the catalyst. The decomposition reaction of 2-HAF using sulfuric acid was successfully modeled (R-2 = 0.9957) using a first-order approach in 2-1-IAF and acid. The activation energy was found to be 98.7 ( 2.2) kJ mol(-1)

Iron Tetrasulfonatophthalocyanine-Catalyzed Starch Oxidation Using H2O2:Interplay between Catalyst Activity, Selectivity, and Stability

Oxidized starch can be efficiently prepared using H2O2 as an oxidant and iron(III) tetrasulfophthalocyanine (FePcS) as a catalyst, with properties in the same range as those for commercial oxidized starches prepared using NaOCl. Herein, we performed an in-depth study on the oxidation of potato starch focusing on the mode of operation of this green catalytic system and its fate as the reaction progresses. At optimum batch reaction conditions (H2O2/FePcS molar ratio of 6000, 50 °C, and pH 10), a high product yield (91 wt %) was obtained with substantial degrees of substitution (DSCOOH of 1.4 and DSCO of 4.1 per 100 AGU) and significantly reduced viscosity (197 mPa·s) by dosing H2O2. Model compound studies showed limited activity of the catalyst for C6 oxidation, indicating that carboxylic acid incorporation likely results from C-C bond cleavage events. The influence of the process conditions on the stability of the FePcS catalyst was studied using UV-vis and Raman spectroscopic techniques, revealing that both increased H2O2 concentration and temperature promote the irreversible degradation of the FePcS catalyst at high pH. The rate and extent of FePcS degradation were found to strongly depend on the initial H2O2 concentration where also the rapid decomposition of H2O2 by FePcS occurs. These results explain why the slow addition of H2O2 in combination with low FePcS catalyst concentration is beneficial for the efficient application in starch oxidation