Valeric Biofuels Research Articles

Enhanced stability of hierarchical zeolite-metal bifunctional catalysts for conversion of levulinic acid to valeric biofuels

Valeric ester has been recognized as a new generation of biofuels with promising environmental advantages. Metal-zeolite bifunctional catalysts demonstrated outstanding performance in tandem transformation including the tandem conversion of levulinic acid to valeric ester via synergetic catalysis of C = C bond hydrogenation and C-O bond cleavage, but still suffering from rapid catalyst deactivation due to coke formation. Herein, a hierarchical HZSM-5 supported Ni catalyst was developed, and displayed efficient ethyl valerate production activity with a catalytic lifetime as long as 180 h, which is 8-fold longer than that of microporous zeolite counterpart (20 h). Notably, this nonprecious Ni catalyst can be stably regenerated by calcination at least four times with its total lifetime up to 900 h. Systematic investigations reveal that the presence of secondary porosity, the less strong acid sites and weaker adsorption of ethyl valerate on hierarchical catalysts could effectively alleviate coke formation and promote catalyst stability. More importantly, the hierarchical porosity of HZSM-5 alters the acid site distribution, enabling more acid sites to be located on the external surface, and thus retards the coverage of the active site by carbonaceous species. Besides, the addition of 10 % ethyl valerate in diesel can reduce the emission of exhaust pollutants, wherein the CO, NOx, HC, and soot emissions can be reduced by 13 %, 5 %, 4 %, and 27 % at an engine speed of 1500 rpm, respectively. This work develops an alternative strategy by tuning pore size and acid distribution to enhance the metal/zeolites catalyst stability against coke deposits and promotes the practical application of ethyl valerate as an environmentally friendly oxygenated additive for the current liquid fuels.

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.

Controlling reaction pathways via selective C-O activation for highly efficient biomass oriented-upgrading

Achieving precise selectivity control by driving specific reaction paths involving selective C-O bond activation of multifunctional molecules in renewable biomass oriented-upgrading is highly attractive but challenging. Herein, a facile in-situ hydrothermal strategy was developed to obtain highly dispersed and stable Cu nanoparticles encapsulated in well-organized HZSM-5 zeolite, which exhibited extraordinary selectivity control in the lignocellulosic biomass-derived γ-valerolactone (GVL) upgrading toward valuable valeric biofuels with good stability. The as-synthesized Cu@HZSM-5 exhibited a framework Al-dependent Cu distribution characteristic in HZSM-5, while the Cu spatial confinement by zeolite framework together with the synergetic effect of confined Cu centers and acidic zeolite support endowed the optimized Cu@HZSM-5 catalysts exceedingly high hydro-conversion efficiency. Theoretical calculations demonstrated that the transferred electrons from Cu to GVL in different zeolite microenvironments (zeolite-encapsulated and -impregnated structure) showed the very distinct redistributions on the C atoms of GVL, which was crucial to tune the ring C-O bond activation mode in GVL ring-opening, consequently giving a well-controlled product selectivity.

Direct cascade hydrogenation of biorenewable levulinic acid to valeric acid biofuel additives over metal (M = Nb, Ti, and Zr) supported SBA-15 catalysts

Chemoselective hydrogenation of biomass platform molecules into value-added chemicals and fuels is essential for the exploitation of biomass, and SBA-15 based metal catalysts with hydrogenation centers and acid sites seem promising in this regard. Valeric acid (VA) is the most important platform molecule for valeric biofuels and value-added chemicals production. The main issue with using such bifunctional catalysts for biomass conversion is maintaining the catalyst's stability in the liquid phase under harsh conditions. In-addition, direct one-pot selective hydrogenation of levulinic acid (LA) into VA synthesis is challenging due to its complex reaction conditions involved. Herein, we design a bifunctional mesoporous catalysts (SBA-15 mesoporous material doped with various metals Nb, Ti, and Zr) investigated for this reaction under the vapour phase. Different instrumental approaches were used to examine the structure, phase composition, morphology, and surface elemental analyses of catalysts as-prepared. Among those catalysts, Zr-doped mesoporous SBA-15 catalyst showed the 91% conversion of LA and the 68% selectivity toward VA and promising stability in a 52 h time on-stream run. Metal dispersion inside the SBA-15 and their surface acidity (sufficient number of acid sites and surface-active metal oxide species) and higher surface area are beneficial for the selectivity of VA. This work offers a highly-efficient bifunctional catalyst for selective hydrogenation of biomass feedstocks.

Recent Advances in Ruthenium-Catalyzed Hydrogenation Reactions of Renewable Biomass-Derived Levulinic Acid in Aqueous Media.

Levulinic acid (LA) is classified as a key platform chemical for the development of future biorefineries, owing to its broad spectrum of potential applications and because it is simply available from lignocellulosic biomass through inexpensive and high-yield production routes. Catalytic hydrogenation reactions of LA into the pivotal intermediate compound γ-valerolactone (GVL), and beyond GVL to yield valeric acid (VA), 1,4-pentanediol (1,4-PDO), and 2-methyltetrahydrofuran (2-MTHF) have gained considerable attention in the last decade. Among the various transition metals used as catalysts in LA hydrogenation reactions, ruthenium-based catalytic systems have been the most extensively applied by far, due to the inherent ability of ruthenium under mild conditions to hydrogenate the keto functionality of LA selectively into an alcohol group to form 4-hydroxyvaleric acid intermediate, which yields GVL spontaneously after dehydration and cyclization. This review focuses on recent advances in the field of aqueous-phase ruthenium-catalyzed hydrogenation reactions of LA toward GVL, VA, 1,4-PDO, 2-MTHF, 2-pentanol, and 2-butanol. It employs heterogeneous catalysts on solid supports, and heterogeneous water-dispersible catalytic nanoparticles or homogeneous water-soluble catalytic complexes with biphasic catalyst separation, for the inter alia production of advanced biofuels such as valeric biofuels and other classes of liquid transportation biofuels, value-added fine chemicals, solvents, additives to gasoline, and to food as well. The significance of the aqueous solvent to carry out catalytic hydrogenations of LA has been highlighted because the presence of water combines several advantages: (i) it is highly polar and thus an ideal medium to convert polar and hydrophilic substrates such as LA; (ii) water is involved as a byproduct; (iii) the presence of the aqueous solvent has a beneficial effect and enormously boosts hydrogenation rates. In sharp contrast, the use of various organic solvents gives rise to a dramatic drop in catalytic activities. The promotional effect of water was proven by numerous experimental investigations and several theoretical studies employing various types of catalytic systems; (iv) the large heat capacity of water renders it an excellent medium to perform large scale exothermic hydrogenations more safely and selectively; and (v) water is a non-toxic, safe, non-inflammable, abundantly available, ubiquitous, inexpensive, and green/sustainable solvent.

Metal regulating the highly selective synthesis of gamma-valerolactone and valeric biofuels from biomass-derived levulinic acid

Highly selective upgrade of biomass-derived source to biofuels is crucial for the utilization of biomass. Herein, we report a strategy for the highly selective conversion of biomass-derived levulinic acid (LA) to gamma-valerolactone (GVL) or valeric biofuels simply by tuning the used metal Ni or Ru on HZSM-5 support. The catalytic experimental results show that 3 wt% Ni/HZSM-5 catalyst achieves high yield (93.1%) of GVL with negligible formation of pentanoic acid (<1% yield) or pentanoic esters (<1% yield), while 3 wt% Ru/HZSM-5 catalyst exhibits a high yield (85.7%) of pentanoic esters (PE) and pentanoic acid (PA) under the identical conditions. It is found that the introduction of Ru into HZSM-5 would increase the strong acidic sites and enhance the ring-opening of GVL intermediate, promoting the formation of PE and PA. In comparison, 3 wt% Ni/HZSM-5 catalyst shows relative lower acidic sites and negligible ring-opening ability of GVL. The metal effect is further confirmed using GVL and 1, 4-dioxane as substrate, respectively. After that, reaction kinetics are investigated in details and a rational pathway is proposed for the metal effect in deciding the product distribution of LA hydrogenation. This work provides a useful guideline to design proper catalyst for the valorization of biomass resources.

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.

Direct Conversion of Levulinic Acid into Valeric Biofuels Using Pd Supported Over Zeolites as Catalysts

A series of Pd-based catalysts was prepared by incipient wetness impregnation over different acidic supports: amorphous SiO2-Al2O3, ZSM5 and beta zeolites. In addition to the effect of the support, other variables like the metal loading (0, 1, 2 and 4 wt%) on ZSM5 were tested in the direct conversion of levulinic acid (LA) to valeric biofuels (valeric acid/ester). The best result, a 92% yield of valeric biofuels, was obtained for a 2 wt% Pd supported on ZSM5 catalyst (2PdZSM5) after 8 h of reaction at 240 °C. Characterization techniques such as FTIR spectroscopy (using deuterated acetonitrile and CO as probe molecules), TEM and XPS were employed to explain this catalytic performance. FTIR spectra with deuterated acetonitrile evidenced the moderate acidity (in terms of concentration and strength) of the 2PdZSM5 catalyst, a desirable feature for the proper realization of this reaction. It has been observed that the acidity of the support favors the Pd dispersion, but it is less relevant for its catalytic properties. Finally, the stability of a representative catalyst was demonstrated under flow conditions for over 90 h, obtaining moderate but stable yields for the 2PdZSM5 catalyst.

Vapor-liquid and liquid-liquid equilibrium modeling of systems involving ethanol, water, and ethyl valerate (valeric acid) using the PC-SAFT equation of state

Valeric biofuels are renewable and environmental friendly fuels whose production avoids the competition with the food industry for edible oils since its route of production uses lignocellulose of residue from crops as raw material. After the reaction steps several purification operations are necessary for the valeric biofuels to meet purity standards. Therefore, it is of utter importance the knowledge of both liquid-liquid (LLE) and vapor-liquid (VLE) equilibrium behavior of species present in the process, such as ethyl valerate, valeric acid, ethanol and water. In this sense, the objective of this work is to provide a general overview for the phase equilibria of the system aforementioned using experimental data collected as background for the thermodynamic modeling. Experimental data concerning to LLE were evaluated at local atmospheric pressure (around 90.9 kPa) and 293.15 K and 318.15 K, while VLE data were collected at several different controlled pressures, ranging from approximately 7 kPa to local atmospheric pressure (around 91 kPa). UNIFAC and PC-SAFT (Perturbed Chain form of the Statistical Associating Fluid Theory) were used to perform the thermodynamic modeling. The results obtained in this work are helpful to prove the importance of carefully evaluate the interactions between the molecules present in the system. Otherwise, the design of unit operations could underestimate the number of stages required for the purification, causing the products to not reach purity specifications.

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.

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...

Screening Method for Fuels in Homogeneous Charge Compression Ignition Engines: Application to Valeric Biofuels

The successful implementation of innovative fuels relies on many factors and requires a precise description of the combustion characteristics. In practice, traditional indicators, such as octane or cetane numbers, are used. Obtaining these numbers however requires a specific setup. Moreover, they are not sufficient to predict the combustion timing for innovative concepts, such as homogeneous charge compression ignition (HCCI). Evaluating and reporting the characteristics of new fuels is therefore challenging. Using a regular diesel engine converted to HCCI operation, we developed a screening methodology to easily characterize and present key features of new fuels. This paper describes the methodology and then applies it to new fuels produced from biomass: valeric biofuels. The methodology presented in this study intends to bridge the work on fundamental chemical kinetics with conventional engine experiments.

Continuous Catalytic Esterification and Hydrogenation of a Levoglucosan/Acetic Acid Mixture for Production of Ethyl Levulinate/Acetate and Valeric Biofuels

A mixture of levoglucosan (LG) and acetic acid (AA), representing water extracted fast pyrolysis oil, was continuously converted to ethyl levulinate (EL) and ethyl acetate (EA) using H-ZSM5 [120–230 °C, 600 psig, 80% ethanol (v/v)]. Fractional conversion of both reactants was 65% or greater at temperatures above 120 °C, and space time yields (STY) approached 140 and 15 g/L-cat/h for EA and EL, respectively, at 180 °C (LHSV = 4.9 h–1). Two potential pathways for EL formation from levoglucosan were apparent, one with glucose and ethyl α-d-glucopyranoside as intermediates and the other with furfural. Adding metal functionality (Ru/H-ZSM5) resulted in the production of valerate biofuels (esters of carboxylic acids C3 or greater; e.g., pentanoic and hexanoic acid ethyl esters) and EA from the mixture in the presence of hydrogen. Conversions for LG and AA using Ru/H-ZSM5 were similar to H-ZSM5, but ethyl levulinate space time yield declined (∼5 g/L-cat/h) as valerate biofuel STY increased (∼10 g/L-cat/h) at an optimum temperature of 180 °C. Our results indicate that valerate biofuels can be produced from levoglucosan (and possibly other sugars) in a continuous single stage, integrated process. However, due to low yields and coke formation, it is clear that ethanol/water ratios, pore size, and acid site type and density must be optimized when coupled with metal functionality for industrial application.

Sustainable conversion of Pinus pinaster wood into biofuel precursors: A biorefinery approach

Pinus pinaster wood was fractionated by aqueous treatments to yield a solution containing hemicellulose-derived saccharides (mainly of polymeric or oligomeric nature) and a solid phase enriched in cellulose and lignin. The solution containing polymeric or oligomeric hemicellulosic saccharides was acidified with sulfuric acid (up to 4wt%) and heated (up to 130°C) to assess the conversion of substrates into sugars. The interpretation of the experimental data was done on the basis of a mechanism involving 10 first-order, kinetic parameters. Almost total saccharification was achieved under a range of operational conditions, and the hydrolyzates presented compositions favorable for their further utilization as fermentation media. The solid phase coming from aqueous processing was mixed with HCl solutions and reacted under microwave irradiation to yield the target products levulinic acid (precursor of valeric biofuels) and formic acid (suitable for fuel cell devices). The effects of the most influential parameters (temperature, reaction time and acid concentration) were assessed by empirical modeling. The highest cellulose conversion into levulinic acid (61.9% of the stoichiometric value as an average) was achieved at 190°C operating for 15min in a medium containing 1wt% HCl.

Selective hydrogenation of levulinic acid to valeric acid and valeric biofuels by a Pt/HMFI catalyst

Valeric acid and valeric biofuels are obtained in high yield by direct hydrogenation of levulinic acid catalyzed by Pt/HMFI under relatively mild conditions (2 or 8 bar H2, 200 °C), driven by cooperation of the metal and support Brønsted acid sites.

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.

From giant reed to levulinic acid and gamma-valerolactone: A high yield catalytic route to valeric biofuels

The acid hydrothermal conversion of a non-food dedicated feedstock – giant reed (Arundo donax L.) – to levulinic acid (LA) was investigated. LA is a versatile intermediate for the production of biofuels and bio-based chemicals. LA was subsequently hydrogenated to γ-valerolactone (GVL), a sustainable liquid and valuable fuel additive and a precursor for the new platform of “valeric biofuels”. The straight production of GVL directly from water slurries of giant reed was studied by adopting bifunctional (acid and hydrogenating) catalytic systems based on Ru/C and niobium oxide or niobium phosphate. Mild reaction conditions (only 0.5MPa of hydrogen and 70°C) are possible for the hydrogenation step. GVL yields up to 16.6wt.% calculated from the starting weight of dry biomass were reached, with an almost complete and selective conversion of the intermediate LA.

Etherification of 5-hydroxymethyl-2-furfural (HMF) with ethanol to biodiesel components using mesoporous solid acidic catalysts

The etherification of 5-hydroxymethyl-2-furfural (HMF) with ethanol is studied over a series of mesoporous silica catalysts (Al-MCM-41 materials with different Si/Al ratio, and zirconia or sulfated zirconia supported over SBA-15) and compared with the behavior of H 2SO 4 and Amberlyst ®15. The observed reaction products were 5-(ethoxymethyl)furan-2-carbaldehyde (EMF), 1,1-dietoxy ethane (DE) and ethyl 4-oxopentanoate (EOP). The selectivity to EMF and EOP is closely related to the presence of Lewis and/or Brønsted acidity on the catalyst, while the formation of DE is probably related to defect sites. The latter, being less reactive, catalyze the side reaction to DE only when strong Lewis and/or Brønsted acid sites are absent. Catalysts with only a strong Brønsted acidity react selectively to form EOP. When strong Lewis acid sites are present in the catalyst, e.g. by introducing ZrO 2 in SBA-15 or when extra-framework isolated Al 3+ sites are present in the mesoporous channels, a high selectivity to EMF was observed. The results indicate that EMF, DE or EOP can be obtained selectively by direct reaction of HMF with bioethanol by tuning the acidity of the catalyst. EMF is a value biodiesel component, but the results also evidence the possibility to obtain selectively EOP in a one-step reaction, opening interesting perspectives to produce valeric biofuels by subsequent selective hydrogenation.

ChemInform Abstract: Recent Advances in the Catalytic Conversion of Cellulose

AbstractReview: ca. 130 refs.

Valeric Biofuels: A Platform of Cellulosic Transportation Fuels

Valeric Biofuels: A Platform of Cellulosic Transportation Fuels