Valerate Esters Research Articles

Valeric Biofuels from Biomass-Derived γ-Valerolactone: A Critical Overview of Production Processes.

This review analyzes critically the production of valeric biofuels from γ-valerolactone, a relevant biomass-derived platform molecule. Initially, the main properties of valeric esters as fuels for spark- and compression-ignition engines are summarized. Then, catalytic routes to valeric esters from γ-valerolactone are meticulously analyzed, describing the acid- and metal-catalyzed reactions taking part in the tandem catalysis. Only works focused on the production of the valeric biofuels were considered, excluding the cases where these esters were observed in minor amounts or as byproducts. The role of the appropriate selection of the support, catalytic species, catalyst preparation and experimental conditions on the valeric ester productivity are thoroughly commented. Finally, some concluding remarks and perspectives are given, mentioning the areas where additional efforts must be done in order to turn the dream of a massive and renewable valeric biofuel production into a reality.

Direct solvent-free selective hydrogenation of levulinic acid to valeric acid over multi-metal [NixCoyMnzAlw]-doped mesoporous silica catalysts

Valeric acid (VA) and valeric esters (VEs) are among the essential platform chemicals derived from bio-levulinic acid (LA). However, synthesizing VA from LA is still challenging due to solvent consumption, precious metals utilization, and catalyst deactivation. Thus, this study developed an efficient direct solvent-free selective hydrogenation reaction of LA to VA using non-noble metal-based catalysts. NixCoyMnzAlw-doped mesoporous silica (NMCAS) catalysts were synthesized using a facile one-pot procedure, with 100% LA conversion and 96.3% VA yield obtained at 200 °C and 3 MPa (H2) over the NMCAS catalyst. Ni-based catalysts provided 100% LA conversion, whereas the Mn-Co-based catalyst exhibited a 79.8% LA conversion. The increase in the selectivity for VA observed with the doping of Mn and Al into the catalysts can be explained by the generation of Brønsted and Lewis acid sites, which facilitated the ring-opening of GVL to form VA. The effects of reaction time, temperature, pressure, and solvent were considered. At elevated temperatures and pressures, the formation of 1,4-PDO, resulting from the CO bond breakage of O-C–O in the GVL ring-opening and the subsequent dehydration-cyclization to 2-methyltetrahydrofuran (MTHF), including the over-hydrogenation of VA to pentanol, was detected. An increase in the partial pressure of hydrogen enhanced the hydrogenation activity, thus producing 2-MTHF and pentanols. The NMCAS catalyst has also been applied with various solvents to study the reaction pathway and produce VEs. This work is the primary example of the direct solvent-free, selective, and high-yield production of VA from LA over non-noble heterogeneous catalysts.

Some Insights into the Use of Heterogeneous Copper Catalysts in the Hydroprocessing of Levulinic Acid

Levulinic acid and its esters are close to being extensively produced through consolidated industrial processes, thus playing a central role in biobased industries producing commodities within the principles of the circular economy. One of the main pathways of levulinic acid and ester valorization is their transformation with hydrogen to obtain γ-valerolactone, valeric esters, 1,4-pentanediol and 2-methyl tetrahydrofuran. These reactions are catalyzed by noble and non-noble metal-based heterogeneous catalysts. The use of an abundant and non-toxic element, such as copper, is advantageous with respect to expensive or harmful metals, such as Rh, Ru, Pt or Ni. In this critical review, we wish to give a deeper insight into research advancements in the last ten years regarding the processing of levulinic acid and its esters with hydrogen using heterogeneous copper catalysts.

Torulaspora delbrueckii Strain Behaviour within Different Refermentation Strategies for Sparkling Cider Production

Torulaspora delbrueckii is known for improving the aroma quality in wine and beer, but information for cider manufacturing is scarce. We explored the behaviour of two commercial strains of T. delbrueckii in apple juice fermentation to produce cider and sparkling cider. The influence of the strain, method, and strain–method interaction on the physicochemical parameters of cider was analysed by enzymatic and chromatographic assays. The data were subjected to an analysis of variance and a principal component analysis. Both strains also showed regular fermentation kinetics under pressure. Ethanol, lactic acid, acetic acid, and glycerol were produced with significant differences between strains and production methods. Then, 26 volatile compounds were identified, with higher alcohols being the quantitatively most abundant group. Strain A was associated with a higher production of methyl butanol, 2-phenyl ethanol, and butyric, propionic, and succinic acid esters, while strain B was associated with higher amounts of hexanoic acid, and acetate and valerate esters. In addition, 13 compounds showed significant differences between methods, and 14 were influenced by the method–strain interaction. Our findings encourage the further investigation of the application of T. delbrueckii as a solo player to produce ciders with a unique flavour.

Tuneable Acidity in Fluorinated Al-SBA-15 Materials for the Esterification of Valeric Acid to Alkyl Valerates.

The acidity of Al-SBA-15 materials functionalized by ball milling with several niobium loadings (0. 25–1 wt.%) as well as with several fluorine loadings (by wet impregnation using NH4F as a precursor) was characterized and materials investigated in the esterification of valeric acid to alkyl valerates. The parent Al-SBA-15 support as well as the modified materials loaded with Nb and/or F have been catalysts synthesized characterized by X-ray diffraction (XRD), N2 physisorption measurements, and diffuse reflection infrared spectroscopy (DRIFT) among others. A special interest was paid on the acidity of the materials that was investigated by temperature-programmed desorption of pyridine. Interestingly, the characterization results for the materials containing fluorine showed up an increase in the acidity strength despite of a reduction in the number of acid sites. The catalytic performance of the as-prepared catalysts was investigated in the microwave-assisted esterification reaction of valeric acid to valerate esters. Thus, while the materials modified with niobium exhibited a lower catalytic activity as compared with the catalytic support (Al-SBA-15), the materials loaded with fluorine either onto Al-SBA-15 or on Nb1%/Al-SBA-15 materials presented enhanced conversion values of valeric acid. Therefore, it can be said that the new acid sites with enhanced strength formed by the incorporation of fluorine boost the esterification of valeric acid with alcohols to form the respective valerate ester.

Transformation of Levulinic Acid to Valeric Biofuels: A Review on Heterogeneous Bifunctional Catalytic Systems.

Valerate esters (VAEs) commonly derived from levulinic acid (LA), which is deemed as one of the most promising biomass platform molecules, have been hailed as "valeric biofuels" in recent years. The cascade transformation of LA to VAEs consists of a series of acid- and metal-catalyzed processes alternately, in which heterogeneous bifunctional catalysts are required for better catalytic performance. The transformation pathway from LA to VAEs is presented, and bifunctional catalytic systems for the cascade transformation of LA into valeric acid (VA) and its esters, as well as one-pot conversion processes, are reviewed. Additionally, effects of metal and acid sites on the catalytic performance are discussed in detail. Impacts of and improvements to coke deposition, which is determined to be the primary reason for the reduction in catalytic activity, are also analyzed. Finally, feasible suggestions are proposed for enhanced catalytic performance and a reduction in overall costs.

Process intensification by microwave irradiation in immobilized-lipase catalysis in solvent-free synthesis of ethyl valerate

Valeric esters are a promising energy source and used in different industries ranging from biofuels, perfumes, food, flavors to pharmaceuticals. Ethyl valerate is one of the esters possessing all these attributes as an industrial chemical. In the current work an enzymatic route was examined using valeric acid and ethanol with commercially available lipases, namely, Lipozyme RM IM, Lipozyme TL IM and Novozyme 435 (Candida antarctica lipase B) under solvent fee condition and microwave irradiation. Novozym 435 could lead to 69.2% conversion of valeric acid at 50 °C using equimolar ratio of valeric acid and ethanol at enzyme loading of 10.06 g L−1 in 40 min under microwave irradiation. Lineweaver-Burk plot shows ternary complex mechanism with inhibition by ethanol. A reaction mechanism is proposed and kinetic rate equation derived. The enzyme is reusable.

Preparation of valeric acid and valerate esters from biomass-derived levulinic acid using metal triflates + Pd/C

The selective conversion of biomass-derived levulinic acid to produce valeric acid and valerate esters was successfully performed in the presence of H2, in which metal triflates and Pd/C were used as the catalysts.

Highly efficient transformation of γ-valerolactone to valerate esters over structure-controlled copper/zirconia catalysts prepared via a reduction-oxidation route

Design and development of novel and efficient catalysts are crucial but challenging for the catalytic conversion of biomass and derivatives to fuels and chemicals. In this paper, a novel separate nucleation and aging steps assistant reduction-oxidation strategy was developed to synthesis CuO/ZrO2 complex precursor with homogeneously distributed Cu and Zr components, which can be used as an ideal precursor for the synthesis of highly dispersed Cu/ZrO2 catalyst. Characterization results revealed that homogeneous dispersion of CuO, high surface area of ZrO2 support with controlled porous structure, and strong interaction between CuO and ZrO2 in CuO/ZrO2 precursor could lead to the enhanced Cu dispersion and the formation of Cu+ active centers. The synthesized Cu/ZrO2 catalysts exhibited excellent catalytic performance (85.4% conversion of GVL and 98.0% selectivity of pentyl valerate) in the catalytic transformation of GVL to valerate esters, more efficient than that of Cu/ZrO2-CP and Cu/ZrO2-CH catalysts prepared via co-precipitation and chemisorption hydrolysis methods, respectively. The superior catalytic performance was mainly attributed to both the cooperation of Cu0 and Cu+ species and the highly dispersed surface Cu0, thereby improving the adsorption and polarization of CO bond in GVL and the following dissociation of H2 to produce active hydrogen for the hydrogenation step during the catalytic transformation of GVL. Moreover, such copper-based catalysts exhibited potential applications in the exploitation and utilization of biomass resources with significantly enhanced efficiency.

Liquid-liquid equilibrium of ternary systems comprising ethyl valerate(1), water(2), ethanol(3) and valeric acid(4)

Valeric biofuels stand for a promising energy source, since they are generated from the refining process of crop residues, which converts lignocellulose into the valeric biofuel (or valeric ester). In order to achieve a high grade valeric ester, several washing steps are required and eventually results in the formation of two liquid phases (water-rich and ester-rich phases). In this context, the objective of this study is the experimental determination of liquid-liquid equilibrium (LLE) concerning chemical species present during the ethyl esterification of valeric acid (valeric acid, ethanol, ethyl valerate and water). Results were obtained for the LLE of ternary systems comprised of binodal curves and tie-lines at atmospheric pressure (91.1kPa) and 293.15K and 318.15K. The experimental values obtained were modelled using NRTL, UNIQUAC and UNIFAC-LL Gibbs energy models. Both NRTL and UNIQUAC models were able to correlate satisfactorily the experimental results, while UNIFAC-LL predictions provided greater deviations.

Increasing esterification efficiency by double immobilization of lipase-ZnO bioconjugate into sodium bis (2-ethylhexyl) sulfosuccinate (AOT)- reverse micelles and microemulsion based organogels

In the present study, we developed double immobilization system for entrapment of lipase to increase overall esterification efficiency. Lipase has been attached on functionalized ZnO (zinc oxide) particles. Fabricated lipase-ZnO conjugates were entrapped into sodium bis (2-ethylhexyl) sulfosuccinate (AOT)-reverse micelles. AOT-reverse micelles containing lipase-ZnO conjugate were further entrapped into microemulsion based organogels (MBGs), prepared from polyvinyl alcohol. These immobilization systems were characterized by fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Double immobilized lipase (i.e. organogels) showed highest stability and esterification activity. Organogel immobilized lipase was therefore further applied for the synthesis of pentyl valerate and ethyl valerate esters in n-hexane. Successfully, 90% of ethyl valerate and 86% of pentyl valerate were synthesized using prepared double immobilization enzyme. Furthermore, the immobilized biocatalyst shows reusability for 10 cycles with meager loss of activity. The present study revealed a promising perspective to overcome the well-known drawbacks of the chemical-catalyzed route.

Role of Surface Cooperative Effect in Copper Catalysts toward Highly Selective Synthesis of Valeric Biofuels

Currently, the catalytic conversion of biomass-derived compounds into biofuels is of great significance in terms of environmental protection and sustainable development. Among them, valeric esters derived from γ-valerolactone (GVL) are regarded as one of the most promising alternatives to fossil fuels. Herein, the highly efficient one-pot transformation of GVL to produce a series of valeric esters was successfully achieved over novel ZrO2-incorporated ZnAl2O4-composite-supported Cu-based catalysts. An extensive investigation gave clear evidence that the incorporation of ZrO2 into composites could lead to the enhanced metal dispersion and surface acidity. Especially, the catalyst with a Zr/Zn mass ratio of 0.2 exhibited the best selectivity of 99% in the transformation of GVL into pentyl valerate to date, together with a comparable conversion of 91% with respect to the Cu-based catalyst previously reported. The superior catalytic performance was attributable to the surface cooperation effect between highly...

Structural and biochemical characterisation of Archaeoglobus fulgidus esterase reveals a bound CoA molecule in the vicinity of the active site.

A new carboxyl esterase, AF-Est2, from the hyperthermophilic archaeon Archaeoglobus fulgidus has been cloned, over-expressed in Escherichia coli and biochemically and structurally characterized. The enzyme has high activity towards short- to medium-chain p-nitrophenyl carboxylic esters with optimal activity towards the valerate ester. The AF-Est2 has good solvent and pH stability and is very thermostable, showing no loss of activity after incubation for 30 min at 80 °C. The 1.4 Å resolution crystal structure of AF-Est2 reveals Coenzyme A (CoA) bound in the vicinity of the active site. Despite the presence of CoA bound to the AF-Est2 this enzyme has no CoA thioesterase activity. The pantetheine group of CoA partially obstructs the active site alcohol pocket suggesting that this ligand has a role in regulation of the enzyme activity. A comparison with closely related α/β hydrolase fold enzyme structures shows that the AF-Est2 has unique structural features that allow CoA binding. A comparison of the structure of AF-Est2 with the human carboxyl esterase 1, which has CoA thioesterase activity, reveals that CoA is bound to different parts of the core domain in these two enzymes and approaches the active site from opposite directions.

ChemInform Abstract: Levulinic Acid Biorefineries: New Challenges for Efficient Utilization of Biomass

AbstractReview: 199 refs.

Acidity-regulation for enhancing the stability of Ni/HZSM-5 catalyst for valeric biofuel production

Valerate esters as a new class of cellulosic transportation fuels showed great industrial prospect. Here we developed a non-noble Ni/HZSM-5 bifunctional catalyst with excellent stability for the cascade transformation of levulinic acid to valerate esters. The acidity-regulation of Ni/HZSM-5 catalyst by potassium addition decreased the strong acidity, meanwhile tuned the proportion of Brönsted acidity/Lewis acidity. Coke analysis indicated that acidity-regulation by potassium addition changed the heavier coke component (alkylated poly-aromatics) to the lighter one (alkylated mono-aromatics), thus effectively prolonged the lifetime of Ni/HZSM-5 catalyst in fixed-bed reactor. The relationship of the nature of coke deposits and the acidity-regulation of catalysts could contribute to intensively understand the catalyst deactivation and the choice of stable catalyst for upgrading of biomass and its platform molecules.

Levulinic Acid Biorefineries: New Challenges for Efficient Utilization of Biomass.

Levulinic acid is a sustainable platform molecule that can be upgraded to valuable chemicals and fuel additives. This article focuses on the catalytic upgrading of levulinic acid into various chemicals such as levulinate esters, δ-aminolevulinic acid, succinic acid, diphenolic acid, γ-valerolactone, and γ-valerolactone derivatives such valeric esters, 5-nonanone, α-methylene-γ valerolactone, and other various molecular-weight alkanes (C9 and C18-C27 olefins).

Compression Ignition and Exhaust Gas Emissions of Fuel Molecules Which Can Be Produced from Lignocellulosic Biomass: Levulinates, Valeric Esters, and Ketones

This paper presents the results of combustion experiments conducted in a single cylinder compression ignition engine with several fuel molecules which can be produced from lignocellulosic biomass through a variety of processing routes. The lignocellulosic fuel molecules tested were ethyl levulinate, butyl levulinate, ethyl valerate, butyl valerate, pentyl valerate, 5-nonanone, 3-heptanone, dipentyl ether and three alkanes. To ensure reliable compression ignition of all of the molecules, all of the molecules were tested after adding 30 wt % of heptane to them. Levulinates were observed to have longer ignition delays than valeric esters, which in turn had longer ignition delays compared to ketones. All of the tested oxygenated molecules ignited later than the corresponding alkanes, excluding dipentyl ether. The differences in ignition delays were mainly attributed to the higher electronegativity of oxygen atoms compared to that of carbon and hydrogen atoms. The tested molecules, excluding 3-heptanone, had s...

Combustion and Emissions Characteristics of Valeric Biofuels in a Compression Ignition Engine

AbstractNew-generation biofuels are mainly produced from nonfood crops or waste. Although second-generation ethanol is one of the main options, valeric esters can also be produced from lignocellulose through levulinic acid. However, only few experimental results are available to characterize their combustion behavior. Using a traditional compression ignition (CI) engine converted to monocylinder operation, the engine performances and emissions of butyl and pentyl valerate (BV and PenV, respectively) were investigated. This paper analyses the experimental results for blends of 20%vol of esters in diesel fuel, taking diesel fuel as the reference fuel. The BV and PenV have a smaller cetane number and consequently the ignition delay of the blends is slightly longer. However, engine performances and emissions are not significantly modified by adding 20%vol of esters to diesel fuel. The BV and PenV then represent very good alternative biofuels for CI engines.

Catalytic conversion of biomass-derived levulinic acid to valerate esters as oxygenated fuels using supported ruthenium catalysts

The development of the catalytic conversion of biomass-based platform molecules into oxygenated fuel molecules is of great significance in order to reduce the dependence on fossil resources and to solve environmental problems. Alkyl valerate esters were proven to have the potential to be renewable additives of gasoline and diesel. In this work, we studied the hydrogenation of levulinic acid (LA) to valerate esters over supported Ru catalysts, and found that the acidity was an important factor for the catalyst performance. A bifunctional catalyst Ru/SBA-SO3H was developed as an active catalyst, and a highest yield of 94% to ethyl valerate (EV) was achieved. The catalyst was characterized by nitrogen adsorption/desorption methods, X-ray power diffraction (XRD), transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The effects of reaction conditions were comprehensively investigated and probable reaction pathways were proposed and verified. The conversion of LA to various alkyl valerate esters can also be catalyzed by the bifunctional catalyst. In addition, supported Cu and Ni catalysts were also screened under similar reaction conditions as Ru-based catalysts, and the combination of Ni/SBA-15 and SBA-SO3H exhibited activity for the conversion of LA to EV.

New generation biofuels: γ-valerolactone into valeric esters in one pot

Ethyl valerate and pentyl valerate, suitable as a gasoline additive and diesel component respectively, can be obtained in a one pot one step reaction from γ-valerolactone, readily available from lignocellulosic biomass. The reaction takes place in ethanol under H2 through nucleophilic addition of the alcohol to the carboxylic group giving hydroxypentanoate, dehydration to pentenoate and hydrogenation to the saturated ester. The bifunctional catalyst used consists of a non noble metal, namely copper, supported on an amorphous weakly acidic material, therefore representing an interesting alternative to Pt–zeolite catalysts. Pentyl valerate can be obtained in one pot with conversions >90% and selectivity up to 83%.