High-density Biofuel Research Articles

Superhydrophobic and superacid magnetic catalyst induced highly selective aldol condensation and alkylation for high-density biofuels

Aldol condensation and hydroxyalkylation/alkylation reactions are the most widely used C–C coupling strategies to synthesize high-density biofuels. But their in-situ generated water is unavoidable and can reduce the acidity of catalyst, thereby inhibiting catalytic activity or triggering side reactions. Herein, novel superhydrophobic and superacid magnetic catalyst Fe3O4@SiO2@F-SO3H is designed and synthesized through simple cladding and chemical grafting. This magnetic catalyst can withstand high temperature up to 215 °C and displays much better superhydrophobicity (contact angle of 155.3°) and lipophilicity (contact angle of 0°) than those of classical Amberlyst-15 and Nafion-212. Notably this catalyst exhibits excellent activity, selectivity and stability for both aldol condensation and hydroxyalkylation/alkylation reactions of lignocellulose derived cyclic ketones and furans. After hydrodeoxygenation, three high-density fuels with density of 0.825, 0.881 and 0.887 g/mL were achieved. This work illustrates an efficient and convenient strategy to achieve high-performance acidic catalyst for synthesizing high-density fuels.

Switching carbon metabolic flux for enhancing the production of sesquiterpene-based high-density biofuel precursor in Saccharomyces cerevisiae

BackgroundSesquiterpenes are designated as a large class of plant-derived natural active compounds, which have wide applications in industries of energy, food, cosmetics, medicine and agriculture. Neither plant extraction nor chemical synthesis can meet the massive market demands and sustainable development goals. Biosynthesis in microbial cell factories represents an eco-friendly and high-efficient way. Among several microorganisms, Saccharomyces cerevisiae exhibited the potential as a chassis for bioproduction of various sesquiterpenes due to its native mevalonate pathway. However, its inefficient nature limits biosynthesis of diverse sesquiterpenes at industrial grade.ResultsHerein, we exploited an artificial synthetic malonic acid-acetoacetyl-CoA (MAAC) metabolic pathway to switch central carbon metabolic flux for stable and efficient biosynthesis of sesquiterpene-based high-density biofuel precursor in S. cerevisiae. Through investigations at transcription and metabolism levels, we revealed that strains with rewired central metabolism can devote more sugars to β-caryophyllene production. By optimizing the MVA pathway, the yield of β-caryophyllene from YQ-4 was 25.8 mg/L, which was 3 times higher than that of the initial strain YQ-1. Strain YQ-7 was obtained by introducing malonic acid metabolic pathway. Combing the optimized flask fermentation process, the target production boosted by about 13-fold, to 328 mg/L compared to that in the strain YQ-4 without malonic acid metabolic pathway.ConclusionThis designed MAAC pathway for sesquiterpene-based high-density biofuel precursor synthesis can provide an impressive cornerstone for achieving a sustainable production of renewable fuels.

A one-pot synthesis of high-density biofuels through bifunctional mesoporous zeolite-encapsulated Pd catalysts

Developing a powerful bifunctional catalyst for tandem reactions is essential to the future carbon neutrality by reducing the energy consumption in chemical industries. Herein, mesoporous zeolite-encapsulated palladium (Pd) nanoparticles (Pd@meso-ZSM-5) synthesized via emulsification-demulsification followed by a dry-gel transformation method were demonstrated to have a remarkable catalytic performance for a one-pot multiple tandem reaction of cyclic ketones (cyclopentanone, cyclohexanone) to bicyclic alkanes (bicyclopentane, bicyclohexane). Compared with supported catalysts (Pd/meso-ZSM-5) and microporous zeolite-encapsulated catalysts (Pd@ZSM-5) with a primary product of monocyclic alkane (cyclopentane, cyclohexane), Pd@meso-ZSM-5 shows much higher catalytic efficiency for the bicyclic alkanes synthesis, which was previously unattainable in the conventional two-step synthesis route. Controlled experiments and detailed characterizations show that mesoporosity provides sufficient space for the generation and diffusion of large molecular intermediates, and the intimate acid-Pd interface promotes the conversion of intermediates. This work proposes a design strategy for a mesoporous zeolite-encapsulated metal catalyst, which efficiently provides cooperative acid-hydrogenation catalysis.

Photosensitized Conia reaction directed synthesis of high-performance asymmetric polycyclic hydrocarbons from biomass-derived ketones and petroleum-derived norbornene

Solar-energy-driven synthesis of high-density biofuels can help to achieve the dual carbon goal of the aviation industry sooner. Herein, a novel photo-Conia strategy was developed for synthesis of high-performance asymmetric polycyclic hydrocarbons from biomass-derived various ketones and petroleum-derived norbornene. The photosensitized Conia reaction mechanism is comprehensively revealed by the combination of monochromatic light excitation, triplet quenching, phosphorescence quenching, Stern-Volmer kinetic analysis and DFT calculations. The photoaddition of cyclopentanone and norbornene has a much faster reaction rate than self-cycloaddition of norbornene, and the green solvent water can promote both the norbornene conversion and the selectivity of monoadduct, along with the optimal norbornene conversion of 94.9 % and monoadduct selectivity of 91.6 %. After hydrodeoxygenation, the hydrocarbon derived from cyclohexanone/norbornene mixture endows high density of 0.941 g∙mL−1 (20.6 % higher than conventional aviation kerosene, 0.78 g∙mL−1) and volumetric net heat of combustion of 40.11 MJ∙L−1, which is much higher than that of classic JP-10 (39.41 MJ∙L−1). Therefore, this work provides a new and eco-friendly route for synthesis of high-performance hydrocarbons using renewable resources (biomass) and renewable energy (solar energy).

Synthesis of renewable C–C cyclic oxygenated compounds dedicated for high-density biofuels from biomass-derived cyclopentanone

Basic magnesium carbonate shows excellent activity for self-condensation of cyclopentanone to yield a biofuel precursor, superior to that of magnesium hydroxide and magnesium carbonate.

Tandem Reactions for the Synthesis of High-Density Polycyclic Biofuels with a Double/Triple Hexane Ring.

Synthesizing high-density fuels from non-food biomass is of great interest in the field of biomass conversion because they can increase the loading capability and travel distance of vehicles and aircraft as compared to conventional low-density biofuels (<0.78 g/cm3). In this work, we reported a new and facile strategy for the synthesis of high-density biofuels with polycyclic structures from lignocellulose-derived 5,5-dimethyl-1,3-cyclohexanedione and different aldehyde derivatives in two steps under mild reaction conditions, including a developed tandem reaction and a hydrodeoxygenation reaction. Theoretical approaches were used to estimate the fuel properties, which indicate that the obtained biofuels have a high density of 0.78–0.88 g/cm3 and high net heat of combustion (NHOC) values of 44.0–46.0 MJ/kg. A representative biofuel 3c was measured to have a high NHOC of 43.4 MJ/kg, which matched well with the calculated NHOC value of 44.4 MJ/kg, indicating the high accuracy of the theoretical approaches. This work is expected to provide a green strategy for the synthesis of polycyclic high-density biofuels with platform chemicals.

Switching Carbon Metabolic Flux for Enhanced Production of Sesquiterpene-Based High-Density Biofuel Precursor in Engineered Yeast

Switching Carbon Metabolic Flux for Enhanced Production of Sesquiterpene-Based High-Density Biofuel Precursor in Engineered Yeast

High-density biofuels production from holistic conversion of microalgal strains through energy-saving integrated approach

The commercial feasibility regarding conversion of the high-solid-loading microalgal suspensions for high-titer biofuels production is questionable owing to incomplete utilization and high processing costs. In this study, the production of multiple highly concentrated biofuels (bioethanol, higher alcohols, and biodiesel) was achieved through cost-effective integrated approach (pretreatment, serial fermentation of carbohydrate/protein, and transesterification of lipid) from highly concentrated (100 g/L) microalgal suspensions (Chlamydomonas mexicana and Chlamydomonas pitschmannii). This integrated approach attained unprecedented total conversion efficiency (48–63%) and maximum total biomass utilization (77–86%) for both the microalgal strains with high yields of bioethanol (0.48 g-ethanol/g-carbohydrate), higher alcohols (0.44 g-higher alcohols/g-protein), and biodiesel (0.82–0.89 g-biodiesel/g-lipid) at suspensions of 100 g/L. Transmission electron microscopy was employed to visualize the changes in the intercellular morphologies before and after serial fermentations. Thus, this study demonstrates a cost-effective and energy-saving integrated approach for the holistic conversion of high-solid-loading microalgal biomass to produce high-density biofuels with minimum waste generation.

Synthesis of renewable C–C cyclic compounds and high-density biofuels using 5-hydromethylfurfural as a reactant

Renewable C–C six-membered ring compound and high-density biofuel are synthesized using 5-hydromethylfurfural as a reactant.

Are fermentation products promising feedstock for high-density bio-fuel? domino reactions for upgrading aqueous acetone–butanol–ethanol mixtures

Upgrading aqueous acetone–butanol–ethanol mixtures to high-density bio-fuels is realized via the three-step domino reaction in a green way.

Highly Efficient Alkylation Using Hydrophobic Sulfonic Acid-Functionalized Biochar as a Catalyst for Synthesis of High-Density Biofuels

Because H2O decreases the acidity of sulfonic acid-based catalysts and initiates catalytic side reactions, the catalytic activity and selectivity of these catalysts are often unsatisfactory in many...

Production of High-Density Fuel Precursor from Biomass-Derived Aromatic Oxygenates: Effect of N2 Pressure on the Alkylation

The alkylation of biomass-derived aromatic oxygenates (anisole, phenol, guaiacol, and m-cresol) with furfural alcohol and 5-hydroxymethylfurfural is a step toward high-density biofuel. Conversion and selectivity trends toward monoalkylated products were evaluated in the presence of different operational conditions in batch process. It was observed that FeCl3 was the best catalytic system for phenol alkylation and produced 84.7% monoalkylated product at 80 °C, for 30 min in a continuous nitrogen flow. Guaiacol, anisole, and m-cresol gave 100%, 79.6%, and 85.5% monoalkylated product, respectively. The effect of nitrogen pressure on alkylation was reported for the first time; the monoalkylated product selectivity of phenol, anisole, m-cresol reached 95.5%, 88.7%, and 100% at 4, 8, and 10 bar of N2 pressure, respectively. The alkylation of 5-hydroxymethylfurfural (5-HMF) with aromatic oxygenates was also studied by replacing furfuryl alcohol with 5-HMF. The selectivity of the monoalkylated product reached alm...

Sulfonic acid functionalized hydrophobic mesoporous biochar: Design, preparation and acid-catalytic properties

Sulfonic acid functional strong acidic catalysts are largely used in various chemical reactions. However, in many reactions with water as product, the catalytic activity and selectivity are unsatisfactory, because hydrophilic acid sites of SO3H would suffer from acidity decreasing and some hydrolysis side reactions would occur via water adsorption. Herein, a novel hydrophobic arenesulfonic acid functionalized biochar was successfully prepared for the first time by one-pot diazo reduction method of biochar with amino-arenesulfonic acid (such as, 4-aminbenzenesulfonic acid, 4-amino-1-naphthalenesulfonic acid, 8-amino-1-naphthalenesulfonic acid, 4-amino-3-hydroxy-1-naphthalenesulphonic acid). It has a large specific surface area of 200–400 m2/g, a hydrophobic network with water contact angle higher than 120° and a higher concentration of sulfonic acid over 1.0 mmol/g. Moreover, the hydrophobicity-oleophilicity and acidity are increased with the arene length and grafting amount of arenesulfonic acid. In the esterification reaction of fatty acid with methanol as well as the transesterification reaction of glycerol trioleate with methanol for the production of biodiesel, the sulfonated biochar shows a higher conversion of 96.7% for esterification and 86.3% for transesterification compared with amberlyst-15 (86.7%, 39.9%) and traditional sulfonation biochar-SO3H (27.4%, 32.6%). In the alkylation reaction of 2-methylfuran with cyclopentanone for the production of high-density biofuel, its catalytic efficiency with target product yield of 76.1% is higher than that of amberlyst-15 (50.2%) and traditional sulfonation biochar-SO3H (13.2%), because of its hydrophobicity and strong acidity. Furthermore, the catalyst is stable and shows an excellent cycle performance after 6 runs. The successful preparation of hydrophobic biochar-based acidic catalysts not only provides a new way for high-value utilization of biochar, but also eliminates the negative effect of water on many catalytic reactions.

Selective Catalytic Route for the Synthesis of High-Density Biofuel Using Biomass-Derived Compounds

A novel strategy for the synthesis of high-density biofuel using two biomass-derived oxygenated compounds, furfural and guaiacol, with a variety of heterogeneous catalysts is proposed. In the first step of this strategy, furfural is converted with high yields and selectivity to cyclopentanol (CPOL) over Mg-Al supported Cu catalysts. Then, the cyclopentanol is used to alkylate guaiacol over a series of HY zeolites to generate C9–C16 oxygenates with an appropriate molecular weight to be used as transportation fuels. Finally, in the last step of this catalytic strategy, the C-alkylation products are successfully hydrodeoxygenated over ruthenium nanoparticles supported on carbon nanotubes (Ru/MWCNT), producing a liquid mixture of cyclic hydrocarbons with high density (0.865 g mL–1 at 20 °C) and excellent low-temperature properties. This overall reaction route is a promising approach for converting biomass-derived compounds into transportation fuel precursors.

Hydrogenated intramolecular cyclization of diphenylmethane derivatives for synthesizing high-density biofuel

Multi-cyclic hydrocarbons from biomass are sustainable alternative for jet fuel. Here we report an unexpected hydrogenated intramolecular cyclization of diphenylmethane derivatives synthesized by alkylation of bio-derived compounds. With the presence of commonly used zeolite-Pd/C dual catalyst, conventional hydrodeoxygenation (HDO) occurs to produce dicyclohexylmethane. However, when only hydrogenation catalysts like Pd/C or Ni is used, novel intramolecular cyclization takes place to produce perhydrofluorene with the selectivity as high as 96.0%. The two pathways were illustrated by step-by-step controlled reactions in detail and a mechanism was proposed to explain the reason for perhydrofluorene formation. Moreover, this intramolecular cyclization is versatile for diphenylmethane with OCH3 or OH group at any position. The synthesized perhydrofluorene shows density of 0.96g/mL, much higher than any biofuels reported and even higher than the widely used high-density fuel JP-10 derived from petroleum. It is believed that this biofuel can be excellent additive to improve the density of other jet fuels.

Synthesis of high-density biofuel with excellent low-temperature properties from lignocellulose-derived feedstock

Converting chemicals that can be derived from lignocellulose to cyclic hydrocarbons is a promising route for the synthesis of high-density biofuels. But the low-temperature properties of most synthesized fuels are not good, with high viscosity and freezing point. Herein, we presented the synthesis of cyclohexane derivatives by the alkylation of aromatic oxygenates (anisole, guaiacol and phenol) with furfural alcohol (furfuryl alcohol and 5-hydroxymethylfurfural), followed with hydrodeoxygenation. It is found that FeCl3 exhibits relatively high activity and selectivity for the alkylation of anisole (guaiacol), and AlCl3 is the best catalyst for phenol. The selectivity of mono-alkylation product is 71.0%, 92.4% and 84.3% for the alkylation of anisole, guaiacol and phenol with furfuryl alcohol when the reactant ratio is 10, respectively. A semi-continuous operation was adopted for the alkylation of furfuryl alcohol to improve the conversion of aromatic oxygenates. When furfuryl alcohol is replaced by 5-hydroxymethylfurfural, the selectivity reaches almost 100%, but the reaction is a little slower and longer time is needed to get full conversion. After hydrodeoxygenation by combination of Pd/C and HZSM-5, the alkylation product was converted to branched cyclohexane with density of 0.804g/cm3 at 20°C, kinematic viscosity of 34.4mm2/s at −60°C and freezing point lower than −80°C, which shows great potential as additive to promote the low-temperature properties of other fuels.

Biosynthesis of β-caryophyllene, a novel terpene-based high-density biofuel precursor, using engineered Escherichia coli

β-caryophyllene is a common sesquiterpene compound currently being studied as a promising precursor for the production of high-density fuels. Acute demand for high-density fuels has provided the impetus to pursue biosynthetic methods to produce β-caryophyllene from reproducible sources. In this study, we produced β-caryophyllene by assembling a biosynthetic pathway in an engineered Escherichia coli strain of which phosphoglucose isomerase gene has been deleted. The 1- deoxy-d-xylulose 5-phosphate (DXP) or heterologous mevalonate (MVA) pathways were employed. Meanwhile, geranyl diphosphate synthase, glucose-6-phosphate dehydrogenase and β-caryophyllene synthase genes were co-overexpressed in the above strain. The final genetically modified strain, YJM59, produced 220 ± 6 mg/L of β-caryophyllene in flask culture. We also evaluated the use of fed-batch fermentation for the production of β-caryophyllene. After induction for 60 h, the YJM59 strain produced β-caryophyllene at a concentration of 1520 mg/L. The volumetric production fermented in the aerobic fed-batch was 0.34 mg/(L·h·OD600) and the conversion efficiency of glucose to β-caryophyllene (gram to gram) was 1.69%. Our results are the first successful attempt to produce β-caryophyllene using E. coli BL21(DE3), and provide a new strategy that is green and sustainable for the production of β-caryophyllene.

Efficient synthesis of high-density aviation biofuel via solvent-free aldol condensation of cyclic ketones and furanic aldehydes

Transferring lignocellulose-derived compounds to cyclic hydrocarbons via aldol condensation has great potential in synthesizing high-density biofuel. But current synthesis involves large amount of solvent that inevitably affects the production efficiency. Herein, we synthesized high-density biofuel efficiently using solvent-free condensation of cyclopentanone/cyclohexanone and furfural/5-hydroxymethylfurfural. It is found that the solvent-free reaction gives much higher conversion than the diluted one does, for example 86.7% vs 62.7% for cyclopentanone/furfural condensation, and the selectivity of condensed product is above 90.0%. The reaction rate slows down when the reactant is changed from cyclohexanone to cyclopentanone or from furfural to 5-hydroxymethylfurfural, but can be improved by simply increases the dosage of catalyst or reaction temperature. As a result, the yield over 85.0% is obtained for the condensation reactions. Subsequently, the condensed products were converted to branched cyclic hydrocarbons with selectivity of about 70–80%. Their density increases from 0.815g/ml to 0.826g/ml with the increase of carbon number, with the freezing point increasing from −24.6°C to −9.5°C. They have very low viscosity and can be used as liquid fuels alone or blended with other fuels.

Highly controllable and selective hydroxyalkylation/alkylation of 2-methylfuran with cyclohexanone for synthesis of high-density biofuel

Catalytic hydroxyalkylation/alkylation of hemicellulose-derived 2-methyfuran with lignin-derived cyclohexanone yields high-density biofuel precursor (FCF) with high yield of 89.1% over nafion-212. The reaction can also be controlled at the hydroxyalkylation stage to produce another precursor (FC) with yield of 76.0% with amberlyst-15 catalyst, low FC/cyclohexanone ratio and the presence of water solvent. After hydrodeoxygenation, two high-density biofuels with density of 0.804g/ml and 0.825g/ml were produced, respectively.

Highly selective self-condensation of cyclic ketones using MOF-encapsulating phosphotungstic acid for renewable high-density fuel

MOF encapsulating catalyst is very selective to transfer biomass-derived cyclic ketones to mono-condensed product through self-condensation and provides great potential for the synthesis of renewable high-density biofuel.