Biofuel Precursors Research Articles

Co-valorisation of cassava peel and rice husk to biofuel precursor via intermediate pyrolysis: Kinetics, thermodynamic and pyrolytic oil characterisation

This study explored the co-valorisation of cassava peel and rice husk into biofuel precursors through pyrolysis. The research involved characterization of the biomass, and thermogravimetric analysis at heating rates of 5, 10, and 15 °C/min. An intermediate pyrolysis was conducted using a laboratory-scale setup with a stainless-steel reactor and a Swagelok double-ended tube, yielding pyrolytic oil for analysis. Proximate analysis revealed cassava peel (CP) contains 9.23 wt% ash, while rice husk (RH) has 16.50 wt% ash respectively, while the combined samples of cassava peel and rice husk (CS) had ash content of 74.27 wt%, fixed carbon of 70.07 wt%, and volatile matter of 75.72 wt%. The heating values for the samples were 17.15 MJ/kg, 15.22 MJ/kg, and 17.06 MJ/kg for cassava peel, rice husk, and combined sample respectively. Ultimate analysis indicated the following elemental compositions: CP (40.95 % C, 5.67 % H, 0.22 % N, 0.09 % S, 52.17 % O2), RH (40.15 % C, 5.98 % H, 0.41 % N, 0.78 % S, 52.68 % O2), and the CS (43.06 % C, 6.41 % H, 0.32 % N, 0.41 % S, 49.80 % O2). Kinetic and thermodynamic analysis from the distributed activation energy models revealed average activation energies of 184.95 kJ/mol (CP), 140.56 kJ/mol (RH), and 125.63 kJ/mol (CS). The pyrolysis products consist of 37.50 wt% pyrolytic oil, 11.12 wt% bio-char, and 51.38 wt% non-condensable gases. GC–MS analysis of the pyrolytic oil identified significant amounts of hydrocarbons, phenols, and phenol derivatives, suggesting potential for biofuel production. This study highlights the viability of combined biomass sources for biofuel production and waste to wealth utilization.

Catalyst screening for conversion of Chlorella sp. to aromatic fuel additives: A sustainable strategy for CO2 capture

Developing biofuels with characteristics similar to current fossil fuels and compatibility with existing petroleum infrastructure (drop-in biofuels) is gaining prominence, aligning with global efforts towards carbon-neutral economies and decarbonization of the transportation sector. The originality of the current study involves two directions: first, the use of Chlorella sp. microalgae, cultivated under simulated post-combustion gas, as a raw material for producing drop-in biofuel precursors; and second, an investigation of the catalytic activity of hierarchical zeolites in the deoxygenation and denitrogenation of volatile pyrolysis products, enhancing hydrocarbon content. To accomplish this, a micro-furnace-type temperature-programmable pyrolyzer coupled with chromatographic separation and mass spectrometry detection (Py-GC/MS) was utilized to assess the upgrading effectiveness of distinct zeolites (faujasite-type, MFI-type, and mordenite-type) on volatile pyrolysis products. All tested zeolites effectively reduced oxygenated and nitrogenated compounds in the volatile pyrolysis products, enhancing their suitability for producing renewable fuel. This supports sustainable development goals by promoting affordable, clean energy and climate action. HMor yielded the highest hydrocarbon content (98.5 %), followed by HZSM-5 (97.6 %) and HY (85.5 %). Catalytic upgrading significantly increased the concentration of aromatic hydrocarbons (at least 66.3 %), with MFI-type zeolites showing the highest selectivity for valuable BETX compounds (benzene, ethylbenzene, toluene, xylene). Hydrocarbons in the gasoline range, with up to 91.7 %, predominantly align with the needs of the transportation fuel market. The principal component analysis illustrates that using MFI-type zeolites promoted the lowest selectivity for PAHs, constituting precursors for coke formation, which is advantageous for ensuring a longer catalyst lifespan. Our results are promising and encourage the conversion of microalgal biomass into renewable fuel additives for formulating drop-in biofuels, as hydrocarbon-rich volatile pyrolysis products could be directly integrated into existing biorefineries. Thus, microalgal biomass cultivated using flue gas as the carbon source can be viewed as a versatile and promising resource for producing renewable fuel additives, contributing to developing a sustainable, low-carbon future.

From cassava peel (Manihot esculenta) to hydrocarbon-rich bio-oil: Catalytic flash pyrolysis as a new valorization route

The valorization of agroindustrial residues for second-generation biofuels has garnered attention due to the increasing demand for low-carbon fuels aligned with transportation sector decarbonization efforts. In this context, cassava processing residues, particularly cassava peel, remain largely unexplored but offer a cheap, abundant, and renewable feedstock that can be converted into hydrocarbon-rich biofuel. Thus, the originality of this study lies in investigating the selective conversion of cassava peel into renewable aromatic hydrocarbons through flash pyrolysis catalyzed by an environmentally friendly MFI-type zeolite synthesized from rice husk ash and diatomite residue. A micro-pyrolyzer interfaced with chromatographic separation and mass spectrometry detection was used to compare the composition of condensable volatile products from catalytic pyrolysis over HZSM-5 with those from catalyst-free pyrolysis. Cassava peel, characterized by high volatile matter content (84.3 %), low ash content (3.19 %), and reasonable energy content (15 MJ kg −1), yielded a high content of valuable platform chemicals, such as carboxylic acids and furans, when subjected to catalyst-free pyrolysis. The catalytic upgrading pyrolysis vapors over the environmentally friendly HZSM-5 catalyst yielded approximately 56.0 % industrially relevant aromatic hydrocarbons and 39.9 % light organic acids. Other strengths of using HZSM-5 in upgrading pyrolysis vapors were its low selectivity for naphthalenes, precursors for coke formation, and the production of hydrocarbons in the gasoline range. Thus, HZSM-5 was an efficient catalyst for promoting deoxygenation and improving hydrocarbon content, with high selectivity for valuable aromatic hydrocarbons. In conclusion, cassava peel showed favorable prospects for conversion into hydrocarbon-rich bio-oil, serving as a valuable precursor for low-carbon biofuels.

Hydrothermal Liquefaction of Organic Waste Model Compounds: The Effect of the Heating Rate on Biocrude Yield and Quality from Mixtures of Cellulose-Albumin-Sunflower Oil.

Hydrothermal liquefaction (HTL) is a promising technology for the conversion of high-moisture biomass into a liquid biofuel precursor without predrying treatment. This study investigated the effects of the heating rate (20-110 °C/min) and feedstock composition on phase repartition of the HTL products. HTL tests were carried out using as feedstocks cellulose, egg albumin, and sunflower oil as model compounds for carbohydrates, proteins, and lipids, alone and in binary mixtures. The biocrude, solid residue, and aqueous phase were characterized in terms of composition and elemental percentage. The effects of binary interactions were studied in terms of product yields and compositions. It was observed that higher heating rates resulted in lower solid yields from all the cellulose-containing feedstocks and, in most cases, in higher biocrude yields and higher energy recovery. The results showed that the heating rate influences also the oil composition. Biocrude and solid yields were compared with their prediction based on the combination of the yields of single model compounds, showing a general increase in biocrude yields and a decrease in solid yields. The most significant deviation is observed with the mixture cellulose-albumin both for the biocrude and solid yields. In fact, the main interactions were recognized for carbohydrate-protein mixtures followed by carbohydrate-lipid and protein-lipid mixtures.

Clostridium carboxidivorans and Rhodosporidium toruloides as a platform for the valorization of carbon dioxide to microbial oils

There is growing scientific interest in oleaginous yeasts producing microbial oils as precursors of biofuels and potential substitutes for fossil fuels. Due to the high cost of substrates commonly metabolized by yeasts, volatile fatty acids (VFAs) are gaining interest as alternative cheap and sustainable carbon sources, which can be obtained from solid, liquid and gas pollutants. In this research, Rhodosporidium toruloides was proven to be able to accumulate microbial oils from VFAs obtained from the fermentation of syngas by Clostridium carboxidivorans. Using CO2 and CO as carbon sources from the syngas mixture and H2 as energy source, this acetogen produced, via the Wood-Ljungdahl pathway, a mixture of acetic, butyric and caproic acids. It was first revealed that R. toruloides exhibited minimal inhibition at concentrations below 12 g/L when exposed to a mixture of VFAs, which included acetic, butyric and even hexanoic acids. The yeast was then grown on the culture medium derived from the acetogenic fermentation of syngas. Between the two yeast strains tested of the same species, R. toruloides DSM 4444 reached a total VFAs consumption of 69.1 g/L, supplied by successive additions of acids to the reactor, yielding a maximum lipid content of 29.7% w/w cell. The lipid profile obtained in this case, in terms of abundance followed the order C18:1 > C16:0 ≥ C18:0 > C18:2>others; in which the dominant compound (C18:1), represented approximately 50% of the total. This research opens new possibilities in the cultivation of oleaginous yeasts for the production of biofuels and bioproducts from C1 gases.

Sustainable catalytic pathways for biofuel precursors: quantitative conversion of glucose to gluconic acid using Pt-Zn biochar catalyst

Achieving quantitative conversion of biomass-derived feedstocks under ambient environmental conditions (20°C, atmospheric air, 0.1 MPa) is a critical milestone for sustainability in chemical processes. Herein, the quantitative conversion of glucose to gluconic acid was accomplished under ambient environmental conditions without any additives using a Pt-Zn intermetallic nanoparticle-supported biochar catalyst prepared from raw rice straw (Pt-Zn/strawC) via a straightforward one-pot solvothermal reaction with ethylene glycol solvent. Spectroscopic analyses verified the formation of the Pt-Zn intermetallic alloy and confirmed strong electronic metal-support interactions. The Pt-Zn/strawC catalyst (Pt:Zn molar ratio of 1:6) was highly selective for the conversion of glucose to gluconic acid, whereas yields as high as 99.9% (98.9% gluconic acid, 1.0% glucaric acid) were reached at 20 oC under base-free and additive-free conditions. Isotope measurements and density functional theory revealed synergistic interactions in the Pt-Zn alloy, wherein the alloy tended to absorb glucose and active O2 into superoxide radical (O2·). This work demonstrates a chemocatalytic method that is practical for environmental conditions and provides a new avenue for sustainable conversion of lignocellulosic biomass to chemical products.

Combined production of biofuel precursors, platform chemicals, and catalyst material from the integral processing of rice bran

This research reports first-time results regarding the complete processing of rice bran through the combination of extraction, processing hydrothermal, sulfonation, and trans-esterification procedures, generating biofuel precursors – fermentable sugars, bio-oil, hydro-char, and methyl esters – platform chemicals, and a catalyst material. Analyzes of XRD, FTIR, BET, SEM, EDS, calorific power, GC, and HPLC were employed for the product characterizations. Concerning the hydrothermal processing, the “temperature” and “biomass/water mass ratio” demonstrated an interesting influence on the results, where the thermal parameter had a greater impact on directing the process to obtain products resulting from the biomass polysaccharides thermal decomposition. At 260 °C, 11.98 and 11.40 g (100 g biomass)−1 of fermentable sugars and platform chemicals were obtained, respectively. At 300 °C, the production of bio-oil and hydro-char were benefited, yielding 10.48 and 30.19 g (100 g biomass)−1 of each component, respectively. The hydro-char-sulfonated catalyst demonstrated an attractive catalytic capacity in esterifying the free fatty acids of the rice bran oil, while simultaneously presenting some difficulty in transesterifying its triglycerides, indicating limitations in the mass transfer of the heterogeneous reaction. Using 4 wt% of catalyst, 90.1 % of the free fatty acids and 60.3 % of the triglycerides contained in the oil were trans-esterified into methyl esters after 6 h, respectively, with no decrease in its catalytic activity being observed after four reuses. This process combination presents an alternative arrangement for the full processing of lignocellulosic and oily biomasses, in addition to representing an approach matchless for the rice bran.

Increased triacylglycerol production in Rhodococcus opacus by overexpressing transcriptional regulators

Lignocellulosic biomass is currently underutilized, but it offers promise as a resource for the generation of commercial end-products, such as biofuels, detergents, and other oleochemicals. Rhodococcus opacus PD630 is an oleaginous, Gram-positive bacterium with an exceptional ability to utilize recalcitrant aromatic lignin breakdown products to produce lipid molecules such as triacylglycerols (TAGs), which are an important biofuel precursor. Lipid carbon storage molecules accumulate only under growth-limiting low nitrogen conditions, representing a significant challenge toward using bacterial biorefineries for fuel precursor production. In this work, we screened overexpression of 27 native transcriptional regulators for their abilities to improve lipid accumulation under nitrogen-rich conditions, resulting in three strains that accumulate increased lipids, unconstrained by nitrogen availability when grown in phenol or glucose. Transcriptomic analyses revealed that the best strain (#13) enhanced FA production via activation of the β-ketoadipate pathway. Gene deletion experiments confirm that lipid accumulation in nitrogen-replete conditions requires reprogramming of phenylalanine metabolism. By generating mutants decoupling carbon storage from low nitrogen environments, we move closer toward optimizing R. opacus for efficient bioproduction on lignocellulosic biomass.

Nanoparticles for the synthesis of bio‐based chemical 5‐Hydroxymethyl furfural from agricultural waste and biomass‐derived carbohydrates‐A review

AbstractThe need for 5‐Hydroxymethylfurfural (HMF) has garnered significant attention owing to its versatile applications in the chemical industry as a precursor for biofuels, pharmaceuticals and fine chemicals. This abstract summarizes a complete review on the synthesis of HMF using heterogeneous catalyst from agriculture waste and various biomass‐derived carbohydrates, focusing on their efficiency, selectivity and industrial feasibility. This review systematically outlines the diverse classes of heterogeneous catalyst employed in HMF production, including titanium dioxide (TiO2), zirconium dioxide (ZrO2), silicon dioxide (SiO2) and aluminium oxide (Al2O3), where the discussion highlights their catalytic mechanisms and intrinsic properties that influence HMF yield, selectivity, stability and reusability. In addition, the impact of reaction parameters such as temperature, pressure, solvent, feedstock composition and catalyst morphology on HMF synthesis has been assessed. This review consolidates the current state‐of‐the‐art methodologies in the synthesis of HMF using various heterogeneous nanoparticle catalysts. © 2024 Society of Chemical Industry (SCI).

Study of two glycosyltransferases related to polysaccharide biosynthesis in Rhodococcus jostii RHA1.

The bacterial genus Rhodococcus comprises organisms performing oleaginous behaviors under certain growth conditions and ratios of carbon and nitrogen availability. Rhodococci are outstanding producers of biofuel precursors, where lipid and glycogen metabolisms are closely related. Thus, a better understanding of rhodococcal carbon partitioning requires identifying catalytic steps redirecting sugar moieties to storage molecules. Here, we analyzed two GT4 glycosyl-transferases from Rhodococcus jostii (RjoGlgAb and RjoGlgAc) annotated as α-glucan-α-1,4-glucosyl transferases, putatively involved in glycogen synthesis. Both enzymes were produced in Escherichia coli cells, purified to homogeneity, and kinetically characterized. RjoGlgAb and RjoGlgAc presented the "canonical" glycogen synthase activity and were actives as maltose-1P synthases, although to a different extent. Then, RjoGlgAc is a homologous enzyme to the mycobacterial GlgM, with similar kinetic behavior and glucosyl-donor preference. RjoGlgAc was two orders of magnitude more efficient to glucosylate glucose-1P than glycogen, also using glucosamine-1P as a catalytically efficient aglycon. Instead, RjoGlgAb exhibited both activities with similar kinetic efficiency and preference for short-branched α-1,4-glucans. Curiously, RjoGlgAb presented a super-oligomeric conformation (higher than 15 subunits), representing a novel enzyme with a unique structure-to-function relationship. Kinetic results presented herein constitute a hint to infer on polysaccharides biosynthesis in rhodococci from an enzymological point of view.

UV-C pretreatment of wastewater-grown algal biomass for recover of biofuel precursors

In the present study, ultraviolet radiation C (UV-C) was used as a pretreatment tool for the optimal recovery of biofuel precursors from algae Chlorella vulgaris. The pretreatment efficiency of UV-C with fixed light intensity (1.173 mWcm−2) on 1.5 gL-1 algal biomass was observed at 0, 0.5, 1, 2, 5, 10, and 20 h of irradiation by measuring the released sugar content and soluble chemical oxygen demand (sCOD). The UV-C pretreated algal cells were also analyzed through impedance spectroscopy, fluorescence microscope, and digital images to assess the degree of cell wall disintegration. The released sugar content reached a maximum of 73.61 mg L-1 at 10 h of exposure, whereas the maximum sCOD of 190 mg L-1 was achieved at 20 h exposure. Image analysis indicated that the chlorophyll content declined exponentially from 7.21 to 0.14 µgmL-1 with UV-C exposure. An increase in UV-C exposure time resulted in decreased impedance and increased conductance. The SYTOX green fluorescence also increased with 10 h of exposure, followed by a decline. Therefore, the cell wall stability gets compromised and the permeability increases with increment in UV-C exposure. This triggers extensive release in cell wall sugar content with exposure. Further exposure destabilizes the cell wall leading to discreet breakage. This breakage disperses internal content to bulk liquid, causing elevated sCOD with reduced sugar content. The present study showed that UV-C to be a potential pretreatment strategy to release precursors to derive biofuels such as biohydrogen, bioethanol and others.

Samarium-doped cobalt metal–organic framework as a versatile catalyst for the conversion of furfural and 2-methylfuran to high-value-added biofuel precursors

Fabrication of a samarium-doped cobalt metal–organic framework (Sm/Co-TTA MOF) for catalysing the conversion of furfural and 2-methylfuran to a biofuel precursor 5,5′-(furan-2-ylmethylene)bis(2-methylfuran) (FMBMF) via hydroxyalkylation-alkylation (HAA).

Aluminum ion intercalation in mesoporous multilayer carbocatalysts promotes the conversion of glucose to 5-hydroxymethylfurfural.

In this study, an efficient modification strategy was proposed by facile loading of trace aluminum ions and p-toluene sulfonic acid (p-TSA) in carbon materials to improve their catalytic activity. p-TSA is then proven to regulate the carbonization process and promote the formation of mesoporous and multilayer structures. The hexa-coordinated aluminum structure is characterized by 1H-27Al solid-state nuclear magnetic resonance (SSNMR) and X-ray photoelectron spectroscopy, which serves as the Lewis-Brønsted acid site in carbocatalysts. Accordingly, the resulting catalyst facilitates a yield of ∼70% for converting glucose to 5-hydroxymethylfurfural (HMF) with a maximum carbon balance of around 91.4% at 150 °C in 6 h. In situ NMR, electrospray ionization mass spectrometry and isotope labeling analysis reveal that the hexa-coordinated aluminum sites promote the isomerization of glucose, and the sulfonic groups facilitate the subsequent dehydration and rehydration of fructose and levoglucosan intermediates. Kinetic models further indicate the decreased energy barrier for glucose conversion over the Al3+/p-TSA intercalated carbocatalyst. This work provides a promising strategy for engineering waste-derived carbocatalysts toward effectively converting carbohydrates to precursors of biofuels and bioplastics.

A novel experimental approach for the catalytic conversion of lignocellulosic Bambusa bambos to bioethanol

Bambusa bambos (B.B) biomass is cellulose rich lignocellulosic material, containing 47.49% cellulose, 17.49% hemicellulose, 23.56% lignin was used as a potential substrate for bioethanol production. The research paper investigates the use of B.B biomass as a substrate for bio-ethanol production through a two-phase catalytic conversion process. Four water-regulated regimes were identified to optimize the conversion of lignocellulosic biomass to biofuel precursors. The catalytic hydrolysis of B.B using CuCl2 was conducted for 10 hours at 110˚C, in aprotic ionic liquid (1-Butyl-3-methylimidazolium chloride) medium. The concentrations of glucose and 5-hydroxymethylfurfural (5-HMF) were measured while varying the amount of water addition. Water played a crucial role in the conversion of cellulose to glucose and 5-HMF by influencing product yields through the interplay of transport properties like heat conduction and viscosity. The highest glucose yield was achieved at 60.82% when operating at a water inclusion rate of 115.72 µL water/h for a duration of 6 hours at 110˚C. On the other hand, the maximum HMF yield was observed as 5.84% at water inclusion rate of 77.15 µL water/h for 5 hours at 110˚C. Yeast mediated glucose fermentation resulted in a bioethanol concentration of 5.5 mg/mL utilizing 15 mg/mL of catalytically produced glucose at a temperature of 30°C. After catalytic hydrolysis, the ionic liquid was also efficiently recycled for a sustainable economy.

Photocatalytic production of a C12 liquid biofuel precursor and H2 by Ni(OH)2-ZnIn2S4 in anaerobic water.

Herein, we presented a bifunctional photocatalytic system for 5-hydroxymethylfurfural (HMF) valorization over Ni(OH)2-modified ZnIn2S4. Instead of forming 2,5-diformylfuran C6 products from conventional HMF aerobic oxidation, C-C coupling C12 products and H2 were produced in anaerobic water, which can be an important liquid fuel intermediate and gaseous energy carrier, respectively. This work could spark more insight for biomass utilization.

Bicarbonate-assisted microalgae cultivation for drinking water RO reject recycling and bioproduct generation

This study undrapes a microalgae-mediated approach for recycling drinking water reverse osmosis (RO) reject with bicarbonate supplementation. Among the tested strains, Chlorella pyrenoidosa exhibited a significantly (p ≤ 0.05) higher biomass growth (760.81 ± 34.24 mg L−1) at 4.0 g L−1 bicarbonate in RO reject. Whereas Scenedesmus sp. showed the maximum biomass yield of 1041.81 ± 33.32 mg L−1 in RO reject without bicarbonate. Moreover, bicarbonate in RO reject promoted biofuel precursor synthesis, with Scenedesmus obliquus and Chlorella sorokiniana acquiring maximum carbohydrate (339.41 ± 13.68 mg L−1) and lipid (1453.57 ± 44.29 mg L−1) yields at 0.5 and 1.0 g L−1 bicarbonate, respectively. The fatty acid methyl ester (FAME) and theoretical methane potential (TMP) analyses showed improved biodiesel quality and biogas yield from bicarbonate-supplemented RO reject-grown microalgal biomass. Thus, the present findings inferred that bicarbonate supplementation to RO reject could be an economically feasible approach for RO reject recycling and microalgae-mediated resource recovery.

Mild production of γ-valerolactone, a biofuel precursor, through the catalytic hydrogenation of a biomass derivative using hydrogen produced by photoelectrochemical water splitting

In this article, an efficient and innovative coupled system that involves hydrogen generation from water and hydrogenation of a biomass derived compound is shown for the first time. We have demonstrated that it is possible to use hydrogen produced from photoelectrochemical water splitting for the hydrogenation of a widely available biomass-derived compound (levulinic acid) into a versatile fuel component and/or precursor (γ-valerolactone). This compound, conversely to hydrogen, can be easily stored and handled. The photoelectrocatalyst selected was a TiO2 nanostructure synthesized by electrochemical anodization. The hydrogen produced was simultaneously used to carry out a hydrogenation reaction to transform levulinic acid into γ-valerolactone. The generated hydrogen was transferred to a catalytic reactor containing an aqueous solution of levulinic acid (LA) in the presence of a Ru based catalyst. Remarkable formation of γ-valerolactone (GVL) was obtained at temperatures as low as 30–60 °C. Yields to GVL of ca. 95 % have been obtained with this novel coupled system at only 60 °C. These results confirm the potential utilization in the biomass valorization of in-situ hydrogen production by photoelectrochemical water splitting.

Biofuels from cyanobacteria -a metabolic engineering approach

The concern about the limited availability of petroleum-based fuels and their role in increasing CO2 levels in the atmosphere has sparked significant attention toward biofuel and bioenergy production. The global pursuit of sustainable energy sources has catalyzed innovative research into alternative biofuel production strategies. Transforming CO2 into usable fuels and chemicals is gaining even more prominence. Cyanobacteria, renowned for their photosynthetic ability, have emerged as promising candidates for biofuel synthesis. Their ability to convert solar energy and carbon dioxide into valuable biofuels makes them a compelling avenue for sustainable energy solutions. Using metabolic engineering principles, researchers have endeavored to optimize cyanobacterial metabolic pathways, enhance photosynthetic efficiency, and redirect carbon flux toward biofuel precursors. Numerous species of cyanobacteria offer genetic and metabolic traits that facilitate manipulation, and their photosynthetic characteristics imply that carbohydrates, fatty acids, and even alcohol could serve as potential renewable sources for biofuels. This review showcases cyanobacteria's ability as a biofuel source and emphasizes the transformative influence of metabolic engineering employed in the creation and production of "cyanofuels”

MOF-catalyzed hydroxyalkylation-alkylation reaction for the controlled synthesis of furan oligomers

Hydroxyalkylation-alkylation (HAA) reaction is a type of C-C coupling technique utilized in the production of furan oligomers, which are potential biofuel precursors. In this study, we present the first application of an acidic MOF, Sulfated MOF-808, in catalyzing the HAA reactions of a series of furan oligomers with high yield and selectivity. Specifically, we focused on the optimization of the HAA between 5-methylfurfural (5-MFUR) and 2-methylfuran (2-MF) by varying different reaction conditions, which afforded a quantitative yield reaching 97% while preventing the self-condensation of 2-MF. The catalyst was also found to be recyclable and can be reused without significant loss in its activity. Lastly, we extended the substrate scope to include benzene-based electrophiles, thereby further proving the versatility of the Sulfated MOF-808 catalyst in the HAA reactions of a variety of starting materials.

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.