A Comparative Study on the Reactivity of Various Ketohexoses to Furanics in Methanol

The acid-catalysed dehydration of the four 2-ketohexoses (fructose, sorbose, tagatose and psicose) to furanics was studied in methanol (65 gL(-1) substrate concentration, 17 and 34 mm sulfuric acid, 100 degrees C) with Avantium high-throughput technology. Significant differences in the reactivities of the hexoses and yields of 5-hydroxymethylfurfural (HMF) and its methyl ether (MMF) were observed. Psicose and tagatose were the most reactive, and psicose also afforded the highest combined yield of MMF and HMF of approximately 55% at 96% sugar conversion. Hydroxyacetylfuran and its corresponding methyl ether were formed as byproducts, particularly for sorbose and tagatose, with a maximum combined yield of 8% for sorbose. The formation of hydroxyacetylfuran was studied through C-13 NMR spectroscopy with labelled sorbose, which provided new insights into the reaction mechanism

Kinetic Study on the Sulfuric Acid-Catalyzed Conversion of d -Galactose to Levulinic Acid in Water

Levulinic acid is an interesting building block for biofuel (additives) and biobased chemicals. It is accessible by an acid-catalyzed reaction of a wide variety of carbohydrates. We here report a kinetic study on the conversion of d-galactose to levulinic acid in aqueous solutions with sulfuric acid as the catalyst. The experiments were carried out in a broad range of temperatures (140-200 °C), initial concentrations of galactose (0.055-1.110 M), and concentrations of sulfuric acid (0.05-1 M). The experimental data were modeled using a power-law approach, and good agreement between the experimental data and the model was obtained. The maximum yield of levulinic acid (54 mol %) was achieved at 130-140 °C, low initial galactose concentrations (0.055 M), and high acid concentrations (1 M). With the kinetic information available, the most suitable reactor configuration was determined, and it is predicted that a continuously stirred-tank reactor is preferred over a plug-flow reactor. The findings presented here may also be applicable to the kinetic modeling of levulinic acid synthesis from more complex biomass sources such as lignocellulosic (woody) and aquatic (e.g., seaweed) biomass

Novel Route to Produce Hydrocarbons from Woody Biomass Using Molten Salts

[Image: see text] The thermochemical decomposition of woody biomass has been widely identified as a promising route to produce renewable biofuels. More recently, the use of molten salts in combination with pyrolysis has gathered increased interest. The molten salts may act as a solvent, a heat transfer medium, and possibly also a catalyst. In this study, we report experimental studies on a process to convert woody biomass to a liquid hydrocarbon product with a very low oxygen content using molten salt pyrolysis (350–450 °C and atmospheric pressure) followed by subsequent catalytic conversions of the liquids obtained by pyrolysis. Pyrolysis of woody biomass in molten salt (ZnCl(2)/NaCl/KCl with a molar composition of 60:20:20) resulted in a liquid yield of 46 wt % at a temperature of 450 °C and a molten salt/biomass ratio of 10:1 (mass). The liquids are highly enriched in furfural (13 wt %) and acetic acid (14 wt %). To reduce complexity and experimental issues related to the production of sufficient amounts of pyrolysis oils for further catalytic upgrading, model studies were performed to convert both compounds to hydrocarbons using a three-step catalytic approach, viz., (i) ketonization of acetic acid to acetone, (ii) cross-aldol condensation between acetone and furfural to C(8)–C(13) products, followed by (iii) a two-stage catalytic hydrotreatment of the latter to liquid hydrocarbons. Ketonization of acetic acid to acetone was studied in a continuous setup over a ceria–zirconia-based catalyst at 250 °C. The catalyst showed no signs of deactivation over a period of 230 h while also achieving high selectivity toward acetone. Furfural was shown to have a negative effect on the catalyst performance, and as such, a separation step is required after pyrolysis to obtain an acetic-acid-enriched fraction. The cross-aldol condensation reaction between acetone and furfural was studied in a batch using a commercial Mg/Al hydrotalcite as the catalyst. Furfural was quantitatively converted with over 90% molar selectivity toward condensed products with a carbon number between C(8) and C(13). The two-stage hydrotreatment of the condensed product consisted of a stabilization step using a Ni-based Picula catalyst and a further deep hydrotreatment over a NiMo catalyst, in both batch setups. The final product with a residual 1.5 wt % O is rich in (cyclo)alkanes and aromatic hydrocarbons. The overall carbon yield for the four-step approach, from pinewood biomass to middle distillates, is 21%, assuming that separation of furfural and acetic acid after the pyrolysis step can be performed without losses

Mechanistic Investigations into the Catalytic Levulinic Acid Hydrogenation, Insight in H/D Exchange Pathways, and a Synthetic Route to d₈-?-Valerolactone

gamma-Valerolactone (GVL) is readily accessible by catalytic hydrogenation of carbohydrate-derived levulinic acid (LA) and is an attractive biobased chemical with a wide range of applications in both the chemical (e.g., as biomass-derived solvent) and the transportation fuel sector. In this study, we used isotopic labeling experiments to provide insights into the catalytic hydrogenation pathways involved in the conversion of LA to GVL under different reaction conditions using water as an environmentally benign solvent and Ru/C as a readily available catalyst. H-2 NMR experiments combined with quantum chemical calculations revealed that deuterium atoms can be incorporated at different positions as well as the involvement of the different intermediates 4-hydroxypentanoic acid and alpha-angelica lactone (alpha-AL). The insight provided by these studies revealed an as of yet unexploited sequential deuteration route to synthesize fully deuterated LA and GVL. The route starts by the conversion of LA to alpha-AL followed by a selective deuteration of the acidic protons of alpha-AL by H/D exchange with D2O. Subsequent ring-opening in D2O (d(2)-AL to d(3)-LA) and exchange of the remaining protons of d(3)-LA via a keto-enol tautomerization by heating in D2O under acidic conditions gives d(8)-LA. Finally, the d(8)-LA is catalytically reduced at low temperature using Ru/C with D-2 in D2O to d(8)-GVL

Catalytic Hydrogenation of Renewable Levulinic Acid to γ-Valerolactone:Insights into the Influence of Feed Impurities on Catalyst Performance in Batch and Flow Reactors

γ-Valerolactone (GVL) is readily obtained by the hydrogenation of levulinic acid (LA) and is considered a sustainable platform chemical for the production of biobased chemicals. Herein, the performance and stability of Ru-based catalysts (1 wt % Ru) supported on TiO2 (P25) and ZrO2 (monoclinic) for LA hydrogenation to GVL is investigated in the liquid phase in batch and continuous-flow reactors using water and dioxane as solvents. Particular attention is paid to the influence of possible impurities in the LA feed on catalyst performance for LA hydrogenation. Benchmark continuous-flow experiments at extended times on-stream showed that the deactivation profiles are distinctly different for both solvents. In dioxane, the Ru/ZrO2 catalyst is clearly more stable than Ru/TiO2, whereas the latter is slightly more stable in water. Detailed characterization studies on spent catalysts after long run times showed that the deactivation of Ru/TiO2 is strongly linked to the reduction of a significant amount of Ti4+ species of the support to Ti3+ and a decrease in the specific surface area of the support in comparison to the fresh catalyst. Ru/ZrO2 showed no signs of support reduction and displayed morphological and structural stability; however, some deposition of carbonaceous material is observed. Impurities in the LA feed such as HCOOH, H2SO4, furfural (FFR), 5-hydroxymethylfurfural (HMF), humins, and sulfur-containing amino acids impacted the catalyst performance differently. The results reveal a rapid yet reversible loss of activity for both catalysts upon HCOOH addition to LA, attributed to its preferential adsorption on Ru sites and possible CO poisoning. A more gradual drop in activity is found when cofeeding HMF, FFR, and humins for both solvents. The presence of H2SO4, cysteine, and methionine all resulted in the irreversible deactivation of the Ru catalysts. The results obtained provide new insights into the (ir)reversible (in)sensitivity of Ru-based hydrogenation catalysts to potential impurities in LA feeds, which is essential knowledge for next-generation catalyst development

Experimental and Kinetic Modeling Studies on the Conversion of Sucrose to Levulinic Acid and 5-Hydroxymethylfurfural Using Sulfuric Acid in Water

We here report experimental and kinetic modeling studies on the conversion of sucrose to levulinic acid (LA) and 5-hydroxymethylfurfural (HMF) in water using sulfuric acid as the catalyst. Both compounds are versatile building blocks for the synthesis of various biobased (bulk) chemicals. A total of 24 experiments were performed in a temperature window of 80–180 °C, a sulfuric acid concentration between 0.005 and 0.5 M, and an initial sucrose concentration between 0.05 and 0.5 M. Glucose, fructose, and HMF were detected as the intermediate products. The maximum LA yield was 61 mol %, obtained at 160 °C, an initial sucrose concentration of 0.05 M, and an acid concentration of 0.2 M. The maximum HMF yield (22 mol %) was found for an acid concentration of 0.05 M, an initial sucrose concentration of 0.05 M, and a temperature of 140 °C. The experimental data were modeled using a number of possible reaction networks. The best model was obtained when using a first order approach in substrates (except for the reversion of glucose) and agreement between experiment and model was satisfactorily. The implication of the model regarding batch optimization is also discussed

Inhibition of Mushroom Formation and Induction of Glycerol Release-Ecological Strategies of Burkholderia terrae BS001 to Create a Hospitable Niche at the Fungus Lyophyllum sp Strain Karsten

<p>We investigated the ecological strategies exerted by the soil bacterium Burkholderia terrae BS001 at the hyphae of the soil saprotrophic fungus Lyophyllum sp. strain Karsten. Recently, this bacterium has been reported to form biofilms around, and to comigrate with, growing hyphae of Lyophyllum sp. strain Karsten. In addition, it was found to be able to utilize fungal metabolites. Here, we extend this work to shed some light on the interactions between the bacterial and fungal partner which allow ecological success for the former. In standing liquid microcosms inoculated with Lyophyllum sp. strain Karsten, we detected, upon prolonged incubation, the formation of a mycelial mat at the liquid-air interface. From this mat, primordia were formed after 4-6 weeks, which eventually resulted in mushrooms. However, upon addition of strain BS001 to the bulk liquid, mushroom formation from the fungal mat was clearly inhibited, as evidenced by (1) the formation of significantly lower numbers of primordia and (2) a delay of the onset of primordia formation. Moreover and importantly, the presence of strain BS001 caused the fungus to secrete large amounts of exudates at the mycelial mat, whereas such exudation was absent from control (uninoculated) or Escherichia coli K12- or Variovorax paradoxus BS64-inoculated microcosms. In the exudates, glycerol was the main carbonaceous component, and this compound could be easily utilized by strain BS001. Thus, in different experimental set-ups with the fungal partner, strain BS001 was shown to grow in the fungal exudates on the mat. The two fungal-interactive phenotypes were specific for B. terrae strain BS001, as the other bacteria used in our study, i.e. E. coli K12 and V. paradoxus BS64, did not exhibit any of these phenomena.</p>

Growth phase significantly decreases the DHA-to-EPA ratio in marine microalgae

Microalgae are the principal producers of long-chain polyunsaturated fatty acids (LC-PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in marine ecosystems. Algae are used in aquaculture systems as direct or indirect feed for zooplankton, filter-feeding mollusks and larval stages of crustaceans and fish. Therefore, it is necessary to select nutrient-rich strains, with high levels of EPA and/or DHA, preferably during the stage of rapid growth. During the course of algal growth (exponential to stationary phase), many microalgal species accumulate lipids, especially triacylglycerols. However, relatively little is known about the effect of growth phase on LC-PUFA accumulation. In the present study, absolute and relative EPA and DHA levels of seven representative species of marine microalgae were determined during different growth phases in batch culture. Four species (Phaeodactylum tricornutum, Thalassiosira weissflogii, Thalassiosira pseudonana and Rhodomonas salina) accumulated fatty acids during growth. In all these species, intracellular EPA levels were higher during the late stationary growth phase than during exponential growth. In contrast, an increase in DHA content was not observed and therefore the DHA-to-EPA ratio was significantly lower in late stationary phase cultures. These results can be used to improve the nutritional value of microalgae cultivated for application in marine aquaculture systems

Efficient Conversions of Macroalgae-Derived Anhydrosugars to 5-Hydroxymethylfurfural and Levulinic Acid:The Remarkable Case of 3,6-Anhydro-d-galactose

Macroalgae or seaweed is considered a renewable and sustainable resource to produce biobased fuels, polymers, and chemicals due to its high content of polysaccharides. Various studies have reported the obtained 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) from seaweeds. However, the source of the saccharides that is responsible for HMF formation, accurate yield data (often only HMF concentrations are given instead of yields on feed), and the reaction pathways (including byproducts) is not well understood. We here report a kinetic study on the conversion of 3,6-anhydro-d-galactose (D-AHG), one of the main building blocks of the polysaccharides in seaweed, to HMF and LA in water using sulfuric acid as a catalyst with the aim to rationalize and optimize the production of HMF and LA from seaweeds. The experiments were carried out in batch at temperatures between 160 and 200 °C using various initial concentrations of D-AHG (0.006-0.06 M) and sulfuric acid (0.0025-0.05 M) as the catalyst. The highest experimental yield of HMF within this range of experimental conditions was remarkably high (61 mol %) and obtained at 160 °C, with a low initial D-AHG concentration (0.006 M) and a low acid concentration (0.0025 M). These findings imply that D-AHG is a very good precursor for the HMF synthesis. Additional experiments outside the experimental window gave an even higher HMF yield of 67 mol %. The highest LA yields were 51 mol % [160 °C, low initial D-AHG concentration (0.006 M), and high acid concentration (0.05 M)]. The experimental data were modeled using a power law approach, and the kinetic model was used to determine reactor configurations giving the maximum yield of HMF and LA. The result showed that a plug flow reactor is favorable to achieve the highest yield of HMF, whereas a continuously ideally stirred tank reactor is the preferable reactor configuration to obtain the highest yield of LA.</p

Novel Route to Produce Hydrocarbons from Woody Biomass Using Molten Salts

The thermochemical decomposition of woody biomass has been widely identified as a promising route to produce renewable biofuels. More recently, the use of molten salts in combination with pyrolysis has gathered increased interest. The molten salts may act as a solvent, a heat transfer medium, and possibly also a catalyst. In this study, we report experimental studies on a process to convert woody biomass to a liquid hydrocarbon product with a very low oxygen content using molten salt pyrolysis (350-450 °C and atmospheric pressure) followed by subsequent catalytic conversions of the liquids obtained by pyrolysis. Pyrolysis of woody biomass in molten salt (ZnCl2/NaCl/KCl with a molar composition of 60:20:20) resulted in a liquid yield of 46 wt % at a temperature of 450 °C and a molten salt/biomass ratio of 10:1 (mass). The liquids are highly enriched in furfural (13 wt %) and acetic acid (14 wt %). To reduce complexity and experimental issues related to the production of sufficient amounts of pyrolysis oils for further catalytic upgrading, model studies were performed to convert both compounds to hydrocarbons using a three-step catalytic approach, viz., (i) ketonization of acetic acid to acetone, (ii) cross-aldol condensation between acetone and furfural to C8-C13products, followed by (iii) a two-stage catalytic hydrotreatment of the latter to liquid hydrocarbons. Ketonization of acetic acid to acetone was studied in a continuous setup over a ceria-zirconia-based catalyst at 250 °C. The catalyst showed no signs of deactivation over a period of 230 h while also achieving high selectivity toward acetone. Furfural was shown to have a negative effect on the catalyst performance, and as such, a separation step is required after pyrolysis to obtain an acetic-acid-enriched fraction. The cross-aldol condensation reaction between acetone and furfural was studied in a batch using a commercial Mg/Al hydrotalcite as the catalyst. Furfural was quantitatively converted with over 90% molar selectivity toward condensed products with a carbon number between C8and C13. The two-stage hydrotreatment of the condensed product consisted of a stabilization step using a Ni-based Picula catalyst and a further deep hydrotreatment over a NiMo catalyst, in both batch setups. The final product with a residual 1.5 wt % O is rich in (cyclo)alkanes and aromatic hydrocarbons. The overall carbon yield for the four-step approach, from pinewood biomass to middle distillates, is 21%, assuming that separation of furfural and acetic acid after the pyrolysis step can be performed without losses