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Abstract

A series of bifunctional USY zeolite catalysts with different Al/Zr ratios were synthesised. The incorporation of Zr into the structure was accomplished after partial dealumination of H-USY. Structural and spectroscopic characterization confirmed the preservation of the zeolite network as well as the isolated incorporation of Zr atoms in Al vacancies, with no evidence of large zirconia domains. The catalytic evaluation in the transformation of xylose in 2-propanol allowed to obtain interesting mixtures of bio-products, and to identify the presence of two competitive routes: the formation of GVL following alternating acid-driven and hydrogen-transfer (MPV) steps, and the retro-aldol condensation of xylose. The extent of each of these two competing reaction cascades is strongly dependent on the Zr loading. Thus, the catalyst with the lowest Al/Zr ratio favours the xylose retro-aldol condensation. When considering furfural as starting substrate, only products involved in the cascade to GVL are obtained. In this case, the incorporation of Zr in the catalyst favoured the MPV reactions, enhancing furfural conversion rate. Thus, increasing concentrations of products coming from the reduction of furfural-furfuryl alcohol, furfuryl 2-propyl ether, lactones-, were detected over Zr-USY samples, with the Zr-USY-3 yielding 13.5% of the final product, GVL. The catalysts are reusable after thermal regeneration at 550. °C.

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... Ideally, a one-pot reaction, avoiding the necessity of intermediate separations and purifications, would be possible when using a single catalyst that fulfils the requirements of each reaction step. While some of the steps require Brønsted acid sites, originating, for instance, from the inclusion of Al in zeolite structures, the MPV reduction of carbonyl groups is essentially promoted by Lewis acid sites, like those coming from the presence of Sn, Hf, Ti and Zr species [12,[41][42][43]. The combination of both acid functionalities within the same heterogeneous catalyst might enable the step-by-step conversion of products to increase the selective one-pot one-catalyst production of GVL as the end product [39]. ...
... However, as the time of operation increases, there is a clear change in the yields towards the different compounds, significantly increasing the yield to intermediate compounds (especially, furfuryl alcohol and ether, FOL + FE) at the expense of drastically reducing the production of GVL. This is a clear indication of a fast catalyst deactivation phenomenon, most likely due to the deposition of carbonaceous compounds, such as humins, whose formation is usually linked to the presence of strong acid sites and which has been previously reported for the furfural and xylose conversion in a batch reactor [43,52]. ...
... This result confirms that the slow activity decrease is reversible through calcination, so it may be caused by the formation of scarce organic deposits over the catalyst surface. Their formation is usually linked to the presence of strong acid sites and has been previously reported for furfural, xylose and levulinic acid conversion in a batch reactor [22,43,52]. However, it must be ...
Article
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The one-pot conversion of biomass-derived platform molecules such as levulinic acid (LA) and furfural (FAL) into γ-valerolactone (GVL) is challenging because of the need for adequate multi-functional catalysts and high-pressure gaseous hydrogen. As a more sustainable alternative, here we describe the transfer hydrogenation of LA to GVL using isopropanol as a hydrogen donor over a Zr-modified beta zeolite catalyst in a continuous fixed-bed reactor. A stable sustained production of GVL was achieved from the levulinic acid, with both high LA conversion (ca. 95%) and GVL yield (ca. 90%), for over at least 20 days in continuous operation at 170 °C. Importantly, the small decay in activity can be advantageously overcome by the means of a simple in situ thermal regeneration in the air atmosphere, leading to a complete recovery of the catalyst activity. Key to this outstanding result is the use of a Zr-modified dealuminated beta zeolite with a tailored Lewis/Brønsted acid sites ratio, which can synergistically catalyze the tandem steps of hydrogen transfer and acid-catalyzed transformations, leading to such a successful and stable production of GVL from LA.
... Zr 3d XPS spectra (Fig. 3-left) reveal a small shift of both Zr 3d signals (5/2 and 3/2) to higher binding energies in the FA-modulated sample, indicating a change of the Zr environment. As a reference, Zr 3d XPS spectrum corresponding to crystalline zirconium oxide [46] is much closer to the spectrum of UiO-66(Zr) than to that of UiO-66(Zr)-FA, which would be in agreement with the partial substitution of terephthalate linkers in close proximity to Zr atoms. A similar behavior has been previously reported in hierarchical Zr-based UiO-66 materials with defects. ...
Article
The production of jet-fuel precursors from furfural (FUR) via aldol-condensation with methyl-isobutyl ketone (MIBK) over a defective UiO-66(Zr) catalyst is presented. The resultant C11 adduct (FuMe) would allow the selective production of branched alkanes in the range of jet fuel via a subsequent hydrogenation/hydrodeoxygenation process. The catalyst is prepared using formic acid as modulator, leading to the incorporation of defects on the microcrystalline structure of the metalorganic framework (MOF) material, which dramatically boosts the catalytic performance in this transformation. Thus, the benchmarking with different commercial solid acid catalysts and Zr-based heterogeneous catalysts has identified the defective MOF, UiO-66(Zr)-FA, as clearly superior. An extensive characterization of the modified catalyst by means of X-ray diffraction (XRD), argon adsorption isotherm, thermogravimetry (TGA), acid titration, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform (DRIFT) of adsorbed deuterated acetonitrile, has confirmed the incorporation of missing-linker and missing-node defects within the structure, enabling to explain the enhancement in the catalytic process. The analysis of the reaction kinetics, together with the optimization of the reaction conditions by means of a response surface methodology (allowing predicting the behaviour of the catalytic system under very different conditions) have identified the temperature as the most relevant parameter affecting the selectivity to FuMe. Thus, under the optimized reaction conditions (130 °C; 4 h; FUR/Cat = 2; MIBK/FUR = 4), outstanding total FUR conversion and FuMe selectivity (∼100%) can be achieved. However, the catalyst gets progressively deactivated in successive catalytic runs under the studied reaction conditions, which is attributed to the formation of organic deposits coming from furfural side reactions.
... The direct production of GVL through this one-pot process offers significantly reduced operating costs by minimizing the need to isolate and purify reaction intermediates. Bifunctional Zr-and Al-containing beta [257,258] and USY [259] zeolite catalysts, and physical mixtures of zeolite HY(2.6) with superparamagnetic FeZrO x nanoparticles show promise for this process [260]. [257]. ...
Chapter
Biorefineries are a new concept in chemical manufacturing in which naturally occurring, sustainable biomass resources such as forestry and agricultural waste are converted to diverse fuel and chemical product streams, akin to the processing of non‐renewable fossil fuels by petrochemical refineries. Polysaccharides are attractive potential feedstocks for biorefineries, with the transformation of C5 and C6 sugars offering routes to the production of fine, bulk, and platform chemicals typically produced via petrochemical routes. The transformation of biomass‐derived building blocks will require different processes to those currently employed in the petrochemical industry, wherein highly functional biomolecules are selectively deoxygenated to their target product, which requires new classes of catalyst that are compatible with hydrophilic, bulky substrates. Here, we review recent advances in the design and development of catalysts and processes for C5–C6 sugar reforming into chemical intermediates and products and highlight the challenges of aqueous phase operation and catalyst evaluation, in addition to process considerations such as solvent and reactor selection.
... The decreased porosity of catalyst particles was demonstrated by the X-ray CT video (movie c, e, decreased from 10.9% to 8.7%), and it was the main reason that the yield of petroleum ether soluble product decreased. In contrast, only a small decrease in the yield of petroleum ether soluble product was measured within five cycles (calcination at 550°C in flowing air for 5 h after every cycle) [66,67]. Based on the X-ray CT video analysis (movie d, f, decreased from 10.9% to 9.5%), the porosity of Co: Zn = 1:3/Off-Al H-beta when calcined after every reaction cycle is only decreased slightly, compared with another method for recycling where the catalyst was calcined after every 3rd reaction cycle. ...
Article
Kraft lignin depolymerization to liquid fuels with high yields is crucial to the comprehensive achievement of sustainable and economic feasibility. Herein, we prepared a bimetallic Co-Zn/Off-Al H-beta catalyst through a two-step post synthesis method composed of dealumination and metal incorporation. The bifunctional Co-Zn/Off-Al H-beta catalyst efficiently converted Kraft lignin to liquid fuels, which was attributable to the synergistic effect of Co hydrogen binding sites and Zn Lewis acid sites on H-beta support. Catalytic hydrogenation with Co:Zn = 1:3/Off-Al H-beta catalyst at 320 °C for 24 hours gave the highest yield of petroleum ether soluble product (81%, mainly monomers and dimers). Under these conditions, the liquefied lignin gave a higher heating value of 33.3 MJ/kg, which is a significant increase from 26.0 MJ/kg of Kraft lignin. The catalyst stability test showed excellent recyclability. This work provides a paradigm of improving lignin depolymerization efficiency via the combined use of Lewis acid and hydrogenation catalyst.
... The ratios of Zr to Al are modified, influencing the distribution of products from xylose using 2-propanol as a solvent, with maximum yields to furfural of 40%, xylose ethers up to 60% and GVL (γ-valerolactone) up to 5%. To increase yields to GVL, furfural was employed as the original reactant, reaching over 13% yield GVL [80]. ...
Article
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Biomass is a plentiful renewable source of energy, food, feed and chemicals. It fixes about 1–2% of the solar energy received by the Earth through photosynthesis in both terrestrial and aquatic plants like macro- and microalgae. As fossil resources deplete, biomass appears a good complement and eventually a good substitute feedstock, but still needs the development of relatively new catalytic processes. For this purpose, catalytic transformations, whether alone or combined with thermal ones and separation operations, have been under study in recent years. Catalytic biorefineries are based on dehydration-hydrations, hydrogenations, oxidations, epimerizations, isomerizations, aldol condensations and other reactions to obtain a plethora of chemicals, including alcohols, ketones, furans and acids, as well as materials such as polycarbonates. Nevertheless, there is still a need for higher selectivity, stability, and regenerability of catalysts and of process intensification by a wise combination of operations, either in-series or combined (one-pot), to reach economic feasibility. Here we present a literature survey of the latest developments for obtaining value-added products using hexoses and pentoses derived from lignocellulosic material, as well as algae as a source of carbohydrates for subsequent transformations.
... The catalytic activity of Ni/DeAl-beta after 4-times recycled can be greatly increased to 48.0% after re- generation by calcination (550 °C in flowing air for 5 h), indicating that catalytic deactivation was mainly due to the deposition of bulky or- ganics, in the present case being lignin and its degradation products ( Song et al., 2017). In contrast, no significant catalytic activity loss of Ni/DeAl-beta catalyst appeared after five successive cycles if the cata- lyst was calcined after every cycle, indicating good recyclability of the catalyst, which is in agreement with the findings of López-Aguado et al. (2018). Therefore, the deposition of bulky organics on the catalyst surface is the main cause of catalyst deactivation. ...
Article
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Chapter
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Chapter
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The optimization of the production of γ-valerolactone (GVL) from furfural (FAL) through a cascade of transformations involving hydrogen transfer and different acid-driven reactions has been tackled by using a bifunctional Zr-Al-beta zeolite as catalyst. The study involved the simultaneous evaluation of the influence of the main reaction parameters affecting the performance of the selected catalyst, including temperature, catalyst loading, furfural concentration and reaction time. An experimental design methodology was applied, aiming to maximize the performance of the catalyst in terms of GVL selectivity and efficient use of the biomass resource (minimizing the non-desired products), herein denoted as “selective productivity”. The effects of the studied reaction parameters on each response factor have been obtained and discussed. The ratio furfural/catalyst appears as the key parameter governing the performance of the catalyst system. Under the optimized reaction conditions, the maximum value achieved for GVL selective productivity is 0.61, corresponding to a SGVL of 70.0% and a productivity of 0.88 gGVL·gCAT⁻¹.
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Zr-SBA-15 Lewis acid catalyst has demonstrated an outstanding catalytic activity in the reduction of several carbonyl compounds by means of Meerwein Ponndorf Verley (MPV) reaction, using several secondary alcohols, and showing a very high selectivity towards the desired products. Special focus was addressed in the catalytic activity of Zr-SBA-15 material in the production of furfuryl alcohol from furfural, which is an important reaction for the lignocellulosic biomass valorization. In this transformation, both the reaction temperature and the i-PrOH:Furfural molar ratio exert a positive influence on the rate of the MPV transformation, with the influence of the former being much higher. i-propyl-furfuryl ether, a by-product resulting from the etherification of the target product with the sacrificing alcohol, is also found together with the main product. The production of this side-product is highly influenced by the reaction temperature, so that low temperatures and high sacrificing alcohol to substrate molar ratios have to be applied to keep its production at low levels.
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The Brønsted-acid catalyzed dehydration of xylose and glucose to furfural and 5-hydroxymethylfurfural (5-HDMF) is known to be facilitated by the Lewis-acid catalyzed isomerization of the aldose to the ketose isomer of the sugars. In this study a number of metal halides were screened for their ability to function as both Bronsted and Lewis acids in aqueous solution. The most selective catalyst for this purpose was found to be SnCl4. Hydrolysis of SnCl4 was observed at various concentrations and temperatures resulting in the production of Brønsted acidic protons in a 3.5:1 ratio to Sn4+ at all SnCl4 concentrations above 60 ºC. As a consequence, there was no need to add a Brønsted acid in order to promote the dehydration of either xylose or glucose. SnCl4-promoted isomerization/dehydration of xylose and glucose at 140 ºC in water resulted in conversions of 55% and 33%, respectively, after 2 h of reaction, and furfural and 5-HMF selectivities of up to 58% and 27%, respectively. Significant conversion of sugars to humins was observed in both cases, and in the case of glucose, degradation of 5-HMF to levulinic and formic acids was also observed. The effects of secondary reactions could be greatly suppressed by extraction of the furanic product as it was produced. Using n-butanol as the extracting agent, xylose and glucose conversions of 90% and 75%, respectively, were observed after 5 h of reaction, and the selectivities to furfural and 5-HMF increased to 85% and 69%, respectively. Small additional increases in the furfural and 5-HMF selectivities were obtained by adding LiCl to the aqueous phase without much effect on the conversion of either sugar. In this case, the selectivities to furfural and 5-HMF were 88% and 72%, respectively, after 5 h of reaction at 140 ºC.
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Sorbitol and xylitol obtained from biomass are considered promising potential sources of both carbon building blocks and energy. We report the efficient and selective conversion of sorbitol, xylitol and other polyols into lactic acid as the major product through homogeneous iridium-NHC catalyzed dehydrogena-tive processes. The proposed reaction mechanism involves base-driven hydrolysis of simple sugars which accounts for the catalyst selectivity observed. In addition, catalyst deactivation pathways are explored and rational catalyst optimization is attempted through fine tuning of the complex.
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Biorefineries convert biomass into bio-based products, which have the potential to replace typical products produced by petroleum refineries. They provide a technology platform to reduce anthropogenic greenhouse gas emissions, increase security of supply and reduce the dependency on crude oil. The biorefinery concept presented in this paper focuses on a combination of (1) organosolv fractionation to produce carbohydrates from lignocellulosic biomass and (2) the furan technology to convert carbohydrates into polyethylene furanoate (PEF), a bio-based alternative to polyethylene terephthalate (PET), and furfuryl ethyl ether (FEE), a bio-based transportation fuel component. The goal of this paper is to determine the mass and energy balances of the production of PET and FEE from lignocellulosic biomass and indicate the benefits, as well as potential bottlenecks in the coupling of organosolv and furan chemistry as a biorefinery concept. Three cases where defined, modeled and analyzed, each focusing on a different approach to combine the organosolv and furan conversion technologies and determine the possibility and degree of integration. Modeling results based on experimental data and expert judgments show that wheat straw, as an example of lignocellulosic biomass, can be converted into PEF and FEE at yields between 20 and 40w/w%, based on total input, while energetic efficiencies are between 30 and 40%. This is comparable or even better compared to other upcoming bio-based processes, e.g. 15-35% yield for second generation bio-ethanol production and 25-50% energy efficiency. The conclusion is that in each of the three cases presented bio-based fuels and plastics can be produced via the furan pathway at efficiencies that constitute a viable option from a technological point of view.
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The one-pot conversion of xylose into GVL in 2-propanol has been achieved over bifunctional Zr- and Al-containing beta zeolite catalysts, prepared via a post-synthetic route, possessing both Brønsted and Lewis functionalities. A GVL yield of 35 mol% was obtained at 190 °C after 48 h.
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The aim of this study was to determine the complete reaction network of xylose decomposition in sub- and supercritical water, including small-molecule intermediates, such as organic acids, which are thought to be the final intermediates in the formation of gaseous products. Solutions of xylose in water were heated under sub- and supercritical conditions in the temperature range of 350-450 °C in a continuous reactor at a controlled pressure of 25 MPa. The intermediates found in the liquid phase were xylulose, furfural, retro-aldol products (glyceraldehyde, glycolaldehyde, dihydroxyacetone, and formaldehyde), and organic acids (acetic and formic acids). The reaction types involved were classified according to Arrhenius behavior: the ionic reaction (not showing Arrhenius behavior in the supercritical region) and the free-radical reaction (showing Arrhenius behavior in the supercritical region). Formic acid was the final intermediate before gasification, while acetic acid and formaldehyde were not gasified in the temperature range of this study.
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A bifunctional Sn-Al-Beta zeolite which possesses isolated Lewis and Brønsted acid sites was prepared by a post-synthesis procedure and applied to the one-pot conversion of furfural to γ-valerolactone (GVL), a value-added chemical. Sn-Al-Beta was capable of catalyzing a cascade of the transfer hydrogenation and hydrolysis of furfural to GVL by the interplay of Lewis and Brønsted acid sites. The degree of dealumination and the tin-incorporation method largely influence the acid properties of the catalyst and the catalyst selectivity. A high yield of GVL up to 60% was obtained with Sn-Al-Beta 7 (Si/Sn = 63 and Si/Al = 473) at 180 °C in 2-butanol.
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Different solid acid catalysts, which include several zeolites, zirconium oxide based catalysts, and materials that contain sulfonic acids, have been evaluated in the dehydration of xylose to furfural in alcohol media. Alcohol media were selected to reduce side reactions, many of which occur in aqueous media. Among the tested alcohols, 2-propanol provided better results and yielded a higher furfural production than ethanol and methanol. Catalyst screening evidenced that small-pore-size zeolites (H-ZSM5) or catalysts that show weak acidity (tungstated zirconia) were unable to promote the desired transformation. Kinetic studies performed for the different types of materials revealed that the nature of the acid sites influenced the catalytic performance of the different solid acids to the extent of conditioning the main reaction pathway for the transformation of xylose into furfural. Thus, whereas Lewis acids seem to promote furfural production by the direct dehydration of xylose, Brønsted-type catalysts lead to alkyl xylosides as intermediates in the overall transformation. Although both types of catalysts provide high furfural yields in short reaction times, especially at high temperatures, commercially available β-zeolite with an adequate combination of Brønsted and Lewis acids sites seems to contain the right physicochemical properties to maximize furfural production.
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It is shown by 27 Al MAS-NMR that, besides tetrahedral framework Al (approximately 60 ppm), extraframework pentacoordinated or tetrahedrally distorted Al (approximately 30-40 ppm), and octahedral extraframework aluminum (approximately 0 ppm), tetrahedral Al in amorphous silica-alumina is formed during the dealumination of Y zeolite, either by steam or by SiCl4 treatment. This silica-alumina shows characteristic hydroxyl groups at 3600-3610 cm-1, with acid strength higher than that of zeolite framework hydroxyls. By mild acid or basic treatments it is possible to change the proportion of the different types of aluminum that affect the cracking of gas-oil. It has been found that in highly steam-dealuminated HY zeolites a radical cracking mechanism increases the formation of C1 and C2 on HY zeolites with less than 5 Al per unit cell.
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Switchgrass was treated by 1% (w/w) H2SO4 in batch tube reactors at temperatures ranging from 140-220 °C for up to 60 minutes. In this study, release patterns of glucose, 5-hydroxymethylfurfural (5-HMF), and levulinic acid from switchgrass cellulose were investigated through a mechanistic kinetic model. The predictions were consistent with the measured products of interest when new parameters reflecting the effects of reaction limitations, such as cellulose crystallinity, acid soluble lignin-glucose complex (ASL-glucose) and humins that cannot be quantitatively analyzed, were included. The new mechanistic kinetic model incorporating these parameters simulated the experimental data with R2 above 0.97. Results showed that glucose yield was most sensitive to variations in the parameter regarding the cellulose crystallinity at low temperatures (140-180 °C), while the impact of crystallinity on the glucose yield became imperceptible at elevated temperatures (200-220 °C). Parameters related to the undesired products (e.g. ASL-glucose and humins) were the most sensitive factors compared with rate constants and other additional parameters in impacting the levulinic acid yield at elevated temperatures (200-220 °C), while their impacts were negligible at 140-180 °C. These new findings provide a more rational explanation for the kinetic changes in dilute acid pretreatment performance and suggest that the influences of cellulose crystallinity and undesired products including ASL-glucose and humins play key roles in determining the generation of glucose, 5-HMF and levulinic acid from biomass-derived cellulose.
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Zr-Beta zeolite was prepared by a two-step post-synthesis method involving dealumination of Al-Beta followed by wet impregnation with Zr(NO3)4. Compared with Zr-Beta formed under fluoride-mediated hydrothermal conditions, the post-synthesized samples had smaller particle size and stronger Lewis acidity. The materials were tested as catalysts for Meerwein–Ponndorf–Verley reduction. In the reduction of 4-tert-butylcyclohexanone, it exhibited the same excellent stereoselectivity toward cis-4-tert-butylcyclohexanol (>99%) as the HF-synthesized Zr-Beta, but had a lower TOF. Because of the higher density of zirconium sites and the nanosized crystallites, it was a more effective catalyst for the MPV reduction of 1,4-cyclohexanedione, bulky aldehydes and aromatic ketones. However, it is more susceptible to poisoning by water adsorption because of its hydrophilic nature. The easily scalable synthesis method allows a faster preparation of metal-substituted Lewis acid zeolites, although differences in textural and chemical properties should be taken into consideration when the material is applied as a catalyst.
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Zr-Beta zeolite is a robust and active catalyst for the Meerwein-Ponndorf-Verley reduction of levulinic acid to ?[gamma]-valerolactone, a versatile intermediate for bio-fuels and chemicals. In a batch reactor, ?[gamma]-valerolactone was formed with a selectivity of > 96 % In a continuous flow reactor, > 99 % yield of ?[gamma]-valerolactone was obtained with a steady space-time-yield of 0.46 molGVLgZr-1h-1 within 87 h, on par with that of noble metal based catalysts. The high activity of this catalyst was attributed to the presence of Lewis acidic sites with moderate strength. Due to the relatively few basic sites, it is not poisoned by the acidic reactant. Its robustness in liquid and gas phase reactions coupled with good thermal stability makes Zr-Beta a green regenerable catalyst that can be used directly on levulinic acid without the need for derivatization.
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γ-Valerolactone, which can be produced from lignocellulosic biomass, has drawn increasing attention recently because of its benign properties and versatile functions. However, the temperature employed for its production is relatively high. In order to save energy, herein, a new transformation process of α-angelica lactone to γ-valerolactone was carried out by using a series of room-temperature ionic liquids as solvents in a batch-type reactor. Among these ionic liquids, [Bmim]PF6 showed the best performance on the selective hydrogenation at 60 °C with a reaction time of 20 min. Interestingly, it was found that the reaction can also take place at a temperature as low as room temperature with complete conversion and nearly 100% selectivity, which greatly reduces the energy required for the production of γ-valerolactone. The reaction system of ionic liquid/catalyst showed good reusability. There was no obvious decrease in conversion and selectivity after 10 uses. Furthermore, the kinetics of the catalytic hydrogenation reaction of α-angelica lactone was studied to elucidate the reaction profile. Systematic kinetics experiments were carried out by varying the reaction temperature from 20 to 100 °C at 4.0 MPa, and the simulated data fits well with the first-order reaction law.
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Alkyl levulinates are biobased chemicals having a strong potential to be used in various applications, substituting current chemicals produced from petro-chemical routes. Dedicated literature has considerably increased in the past five years. This review describes state-of-the-art preparation routes and their main application fields. Alkyl levulinates are obtained in high yields and selectivities from simple biomass-derived products like levulinic acid or furfuryl alcohol. They are also obtained directly from lignocellulosic resources with generally limited yields. In all cases, the transformation needs a catalyst. Current efforts are now performed with developing efficient and recyclable catalysts. Alkyl levulinates found applications as solvents and additives as well as in the area of chemical synthesis. The development of new preparation routes and applications of alkyl levulinates are contributing to future greener and sustainable processes.
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Alkyl gamma-hydroxypentanoates and gamma-valerolactone are promising platform chemicals that can be produced from alkyl levulinates in the lignocellulosic biorefinery. Accordingly, this report aims to provide in-depth insight into the molecular aspects involved in the conversion of alkyl levulinates by H-transfer catalyzed by Raney Ni and using 2-propanol as an H-donor and solvent. We demonstrate this methodology as a highly flexible approach in regard to the high degree of control over the product selectivity. In fact, up to 90% yield of alkyl gamma-hydroxypentanoates is obtained at temperatures as low as 298 K. In turn, 94% yield of gamma-valerolactone is achieved at 393 K. In order to shed light on the fundamental aspects of this chemical route, we address: (1) the energetics of the transfer vs. conventional hydrogenation of methyl levulinate, (2) the thermal stability of methyl gamma-hydroxypentanoate in the absence and in the presence of solid catalyst, and (3) the stability of Raney Ni in the conversion of several alkyl levulinates. Lastly, a process concept based on the current results is also proposed. This concept provides a comprehensive overview of the practical possibilities of this process as part of the lignocellulose-based biorefineries. (c) 2013 Elsevier B.V. All rights reserved.
Article
The former synthesis of TS-1 opened new catalytic opportunities for zeolites, especially for their application as selective redox catalysts in several fine chemistry processes. Interestingly, isolated Ti species in the framework positions of hydrophobic zeolites, such as high silica zeolites, offer unique Lewis acid sites even in the presence of protic polar solvents (such as water). Following this discovery, other transition metals (such as Sn, Zr, V, Nb, among others) have been introduced in the framework positions of different hydrophobic zeolitic structures, allowing their application in new fine chemistry processes as very active and selective redox catalysts. Recently, these hydrophobic metallozeolites have been successfully applied as efficient catalysts for several biomass-transformation processes in bulk water. The acquired knowledge from the former catalytic descriptions in fine chemistry processes using hydrophobic Lewis acid-containing zeolites has been essential for their application in these novel biomass transformations. In the present review, I will describe the recent advances in the synthesis of new transition metal-containing zeolites presenting Lewis acid character, and their unique catalytic applications in both fine chemistry and novel biomass-transformations.
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Lignocellulosic biomass typically contains more than 50 wt% sugars that can be upgraded to valuable platform molecules, such as levulinic acid (LA) and gamma-valerolactone (GVL). This article focuses on upgrading GVL produced from lignocellulosic biomass to various chemicals and fuels, such as polymers, fuel additives, and jet fuel. We also review the use of GVL as a solvent for biomass processing, which led to significant improvements in product yields and a more simplified process for producing biomass-derived chemicals such as LA, furfural, and hydroxymethylfurfural.
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A biorefinery that supplements its manufacture of low value biofuels with high value biobased chemicals can enable efforts to reduce nonrenewable fuel consumption while simultaneously providing the necessary financial incentive to stimulate expansion of the biorefining industry. However, the choice of appropriate products for addition to the biorefinery's portfolio is challenged by a lack of broad-based conversion technology coupled with a plethora of potential targets. In 2004, the US Department of Energy (DOE) addressed these challenges by describing a selection process for chemical products that combined identification of a small group of compounds derived from biorefinery carbohydrates with the research and technology needs required for their production. The intent of the report was to catalyze research efforts to synthesize multiple members of this group, or, ideally, structures not yet on the list. In the six years since DOE's original report, considerable progress has been made in the use of carbohydrates as starting materials for chemical production. This review presents an updated evaluation of potential target structures using similar selection methodology, and an overview of the technology developments that led to the inclusion of a given compound. The list provides a dynamic guide to technology development that could realize commercial success through the proper integration of biofuels with biobased products.
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We propose that γ-valerolactone (GVL), a naturally occurring chemical in fruits and a frequently used food additive, exhibits the most important characteristics of an ideal sustainable liquid, which could be used for the production of both energy and carbon-based consumer products. GVL is renewable, easy and safe to store and move globally in large quantities, has low melting (−31 °C), high boiling (207 °C) and open cup flash (96 °C) points, a definitive but acceptable smell for easy recognition of leaks and spills, and is miscible with water, assisting biodegradation. We have established that its vapor pressure is remarkably low, even at higher temperatures (3.5 kPa at 80 °C). We have also shown by using 18O-labeled water that GVL does not hydrolyze to gamma-hydroxypentanoic acid under neutral conditions. In contrast, after the addition of acid (HCl) the incorporation of one or two 18O-isotopes to GVL was observed, as expected. GVL does not form a measurable amount of peroxides in a glass flask under air in weeks, making it a safe material for large scale use. Comparative evaluation of GVL and ethanol as fuel additives, performed on a mixture of 10 v/v% GVL or EtOH and 90 v/v% 95-octane gasoline, shows very similar properties. Since GVL does not form an azeotrope with water, the latter can be readily removed by distillation, resulting in a less energy demanding process for the production of GVL than that of absolute ethanol. Finally, it is also important to recognize that the use of a single chemical entity, such as GVL, as a sustainable liquid instead of a mixture of compounds, could significantly simplify its worldwide monitoring and regulation.
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Al-free Zr-beta zeolite with Si/Zr up to 75 was synthesized in a fluoride medium. The incorporation of zirconium into zeolite beta induced the formation of increased amounts of polymorph B. Lewis acid sites were predominant in the Al-free Zr-beta. Zr-zeolite beta was found to be an excellent catalyst in the Meerwein–Ponndorf–Verley (MPV) reduction of several alkyl- and aryl-substituted cyclohexanones, with high selectivity to the corresponding alcohols. The catalyst was reusable and no leaching was detected under the reaction conditions. A prominent feature of the Zr-zeolite beta catalyst is its ability to maintain activity even in the presence of rather significant amounts of water, up to 9 wt%. The activity was unaffected by the presence of pyridine but was decreased by added acids. However, the poisoning effect could be easily reversed by washing. The excellent performance of Zr-zeolite beta in the MPVO reaction is due to an appropriate Lewis acidity and the ease of ligand exchange at the Zr active sites within the zeolite beta pore channels.
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Take the straight path: Furfural was converted into γ-valerolactone (GVL) through sequential transfer-hydrogenation and hydrolysis reactions catalyzed by zeolites with Lewis and Brønsted acid sites. Together, Zr-Beta and Al-MFI nanosheets generated GVL in 78 % yield without the use of precious metals or molecular H2 . This system offers an attractive streamlined strategy for the production of GVL from biomass-derived molecules.
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An economical and sustainable transfer hydrogenation for aldehydes and ketones is described. The general protocol is mild, chemo-selective and, importantly, uses neither precious nor non-precious metals and even no ligands.
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Reaction pathways for the acid-catalyzed conversion of furfuryl alcohol (FAL) to ethyl levulinate (EL) in ethanol were investigated using liquid chromatography-mass spectrometry (LC-MS), 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, and ab initio high-level quantum chemical (G4MP2) calculations. Our combined studies show that the production of EL at high yields from FAL is not accompanied by stoichiometric production of diethyl either (DEE), indicating that ethoxymethyl furan (EMF) is not an intermediate in the major reaction pathway. Several intermediates were observed using an LC-MS system, and three of these intermediates were isolated and subjected to reaction conditions. The structures of two intermediates were elucidated using 1D and 2D NMR techniques. One of these intermediates is EMF, which forms EL and DEE in a secondary reaction pathway. The second intermediate identified is 4,5,5-triethoxypentan-2-one, which is analogous to one of the intermediates observed in the conversion of FAL to LA in water (i.e. 4,5,5-trihydroxypentan-2-one). Furthermore, conversion of this intermediate to EL again involves the formation of DEE, indicating that it is also part of a secondary pathway. The primary pathway for production of EL involves solvent-assisted transfer of a water molecule from the partially detached protonated hydroxyl group of FAL to a ring carbon, followed by intra-molecular hydrogen shift, where the apparent reaction barrier for the hydrogen shift is relatively smaller in ethanol (21.1 kcal/mol) than that in water (26.6 kcal/mol).
Article
Solubility of six different carbohydrates in methanol, ethanol, 1-propanol, and 2-propanol were measured at 22, 30, and 40°C. Ketose sugars (fructose, tagatose, and lactulose) show higher solubilities than aldoses (glucose, galactose, and lactose). The binary solid–liquid equilibrium data obtained was satisfactory represented by using the A-UNIFAC model. Additionally, the capability of the model to predict the carbohydrate solubility in alcohol–alcohol and alcohol–water mixed solvents was explored. © 2007 American Institute of Chemical Engineers AIChE J, 2007
Article
The dealumination of USY (ultrastable Y) zeolites by nitric acid and oxalic acid treatment was systematically investigated by multinuclear solid-state NMR and MQ MAS NMR experiments. The results show that both acids are very effective in removing non-framework Al as well as framework Al but that aluminum is extracted from the lattice at a higher rate by oxalic acid even at low concentrations. The presence of different species (e.g. silanol nest, Al–OH, four-coordinated framework Al, six-coordinated framework Al, six-coordinated non-framework Al and five-coordinated non-framework Al) was detected, and their changes were followed during the dealumination. The investigation gives evidence that the breakdown of the parent USY zeolite mainly depends on the degree of dealumination and that non-framework Al exerts a great effect on the acidity of the USY zeolite. Leaching-induced increase in the Brønsted acidity of the USY zeolite was also observed by 1 H MAS NMR spectroscopy. The different distribution of Al species in these samples accounted for the different catalytic performance of n-dodecane cracking. © 2002 Published by Elsevier Science B.V.
Article
The aim of this work deals with the development of new approaches to the production of furfural from xylose. It combines relatively cheap heterogeneous catalysts (Amberlyst 70) with simultaneous furfural stripping using nitrogen under semi-batch conditions. Nitrogen, compared to steam, does not dilute the vapor phase stream when condensed. This system allowed stripping 65% of the furfural converted from xylose and almost 100% of selectivity in the condensate. Moreover, high initial xylose loadings led to the formation of two water-furfural phases, which could reduce further purification costs. Constant liquid-vapor equilibrium along stripping could be maintained for different xylose loadings. The modeling of the experimental data was carried out in order to obtain a liquid-vapor mass-transfer coefficient. This value could be used for future studies under steady-state continuous conditions in similar reaction-systems.
Article
Cellulosic biofuel: Ethyl levulinate is a promising biofuel that can be obtained from lignocellulosic residues. A byproducts, furfural, can be converted into ethyl levulinate in an acid-based process. Here, the use of solid acid catalysts for the conversion of furfuryl alcohol into ethyl levulinate is reported. Furfural, a potential coproduct of levulinic acid, can be converted into levulinic acid via hydrogenation to furfuryl alcohol and subsequent ethanolysis to ethyl levulinate. The ethanolysis reaction is known to proceed in the presence of H2SO4. We show here that several strongly acidic resins are comparably effective catalysts for this reaction. Optimal performance is achieved by balancing the number of acid sites with their accessibility in the resin. Acidic zeolites such as H-ZSM-5 also catalyze this reaction, although with a lower activity and a higher coproduction of diethyl ether.
Article
Recently, it was reported that furfuryl ethyl ether is an important flavor compound indicative of beer storage and aging conditions. A study of the reaction mechanism indicates that furfuryl ethyl ether is most likely formed by protonation of furfuryl alcohol or furfuryl acetate followed by S(N)2-substitution of the leaving group by the nucleophilic ethanol. For the reaction in beer, a pseudo-first-order reaction kinetics was derived. A close correlation was found between the values predicted by the kinetic model and the actual furfuryl ethyl ether concentration evolution during storage of beer. Furthermore, 10 commercial beers of different types, aged during 4 years in natural conditions, were analyzed, and it was found that the furfuryl ethyl ether flavor threshold was largely exceeded in each type of beer. In these natural aging conditions, lower pH, darker color, and higher alcohol content were factors that enhanced furfuryl ethyl ether formation. On the other hand, sulfite clearly reduced furfuryl ethyl ether formation. All results show that the furfuryl ethyl ether concentration is an excellent time-temperature integrator for beer storage.