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From levulinic acid biorefineries to γ-valerolactone (GVL) using a bi-functional Zr-Al-Beta catalyst
Abstract
The integration of GVL production in a lignocellulosic biorefinery where furfural and levulinic acid are co-produced is investigated in a one-pot process over Zr-Al-Beta bi-functional catalyst. Under the synthesis and reaction conditions previously optimized for the transformation of furfural, the yield to GVL for the different mixtures of levulinic acid-furfural over this catalysts is very high (60-90 %). The conversion of the reagents (both furfural and levulinic acid) is total after 2 hours of reaction. As the percentage of levulinic acid in the mixture increases, higher yields to GVL are obtained. The results indicate the presence of a synergistic effect due to an improvement of the catalyst stability against furfural-deactivation phenomena. In addition, the mass balances obtained are high, evidencing an efficient use of both platform molecules. An optimization of the transformation of levulinic acid into GVL has shown that it is possible to work with highly concentrated reaction media, allowing excellent productivities of GVL per gram of catalyst (levulinic acid concentration of 300 g·L–1 , catalyst loading = 12.5 g·L–1) leading to a GVL productivity of up to 8 gGVL·gCAT-1 after 6 h at 190 ºC. Under these conditions, a pseudohomogeneous kinetic model has been fitted to experimental data. Also remarkable is that the Zr-Al-Beta catalyst is stable and reusable in this transformation, since no activity loss was evidenced after repeated reaction cycles without any kind of regeneration treatment.
... The amount of non-detected (ND) products ( Figure 7H) increases along the reaction time, which is directly related to the existence of undesired reactions because of the polymerization of FUR or FOL in the presence of acid catalysts [33,60]. Among the Nb-based catalysts, those with longer channels (Nb-Si-RT and Nb-Si-HT) also display a higher proportion of non-detected products, attaining a maximum value of 37% after 24 h at 170 • C. The length of these channels can favor their partial blockage, causing diffusional problems. ...
... As previously stated, these catalysts show a higher proportion of Lewis acid sites compared to Brönsted ones, which would imply that the etherification of FOL to obtain IpFE must take place on Lewis acid sites [26]. Because of the low proportion of Brönsted acid sites, the formation of IpL is limited, since this product requires longer reaction times, being its yields relatively low in comparison to other catalysts, such as Zr-based catalysts [58,60]. On the other hand, it is also noteworthy that both catalysts display a similar proportion of non-detected products at different reaction times. ...
... When IpL is used as feedstock, the conversion values are much lower compared to FUR and FOL, so it seems that its lactonization to form GVL is a thermodynamically limited step in the one-pot process, which agrees with previous studies with Zr-based catalysts [58,60]. On the other hand, it is also noteworthy that the amount of non-detected products is more limited in comparison to the other reactants, confirming that FUR and FOL are highly reactive and responsible for the formation of carbonaceous deposits on the catalyst surface. ...
Nb-based catalysts supported on porous silica with different textural properties have been synthesized, characterized, and tested in the one-pot reaction of furfural to obtain valuable chemicals. The catalytic results reveal that the presence of fluoride in the synthesis, which limits the growing of the porous silica, limits diffusional problems of the porous silica, obtaining higher conversion values at shorter reaction times. On the other hand, the incorporation of NbOx species in the porous silica provides Lewis acid sites and a small proportion of Brönsted acid sites, in such a way that the main products are alkyl furfuryl ethers, which can be used as fuel additives.
... Для реакций, протекающих в жидкой фазе на твердом катализаторе, важным фактором является пористая структура катализатора, поскольку узкие поры могут затруднять транспорт реагентов к активным центрам и отвод продуктов из зерна катализатора, что в конечном итоге приводит к диффузионным затруднениям [14]. Кроме процессов диффузии важную роль в реакции дегидрирования играют кислотные свой ства применяемого катализатора [15], повышение которых может приводить к образованию нежелательного продукта диизопропилового эфира [16]. ...
... В большинстве исследований РВП-гидрирования ЛК до ГВЛ проводят в диапазоне температур 150-220 °C [4]. При сравнительно низких температурах (<150 °C) процесс в зависимости от каталитической системы может протекать с малой селективностью по отношению к ГВЛ [16,22]. Более высокие температуры способны приводить к разрушению растворителя-донора водорода (в нашем случае -изопропанола) благодаря реакции дегидрирования, протекающей на оксидах титана, циркония и церия (>200 °C). ...
... Первая серия экспериментов была направлена на определение влияния температуры проведения процесса на конверсию левулиновой кислоты и селективность по отношению к ГВЛ, донора водорода и наличии конкурирующей реакции в системе [16]. ...
Two series of ZrO 2-containing catalyst varied in textural and acidic properties were synthesized: 1) mesoporous composites on SBA-15 (fabricated by co-precipitation and layer-by-layer deposition of Zr); 2) bulk ZrO 2 (prepared by precipitation (monoclinic) and template method (inverse opals)). The catalysts were characterized by (TEM, SEM, UV and IR spectroscopy, XRF, N 2 adsorption, pH pzc) and tested in levulinic acid to gamma-valerolactone conversion in a hydrogen-donor solvent-isopropanol, via hydrogen transfer by the Meerwein-Ponndorff-Werley mechanism. For ZrO 2-containing catalysts based on SBA-15, zirconium content and catalyst acidity turned out to be activity-determining properties. An increase in the catalyst acidity with a zirconium content reduction leads to a rise in the substrate conversion rate and a decrease in the GVL selectivity. The maximum GVL yield was 94 mol.% (190 °C, 120 min.) on the Zr/SBA-15(2) catalyst fabricated by double layering of zirconia onto a mesoporous silica matrix. The activity of bulk ZrO 2 turned out to be significantly lower, providing the maximum GVL yield 50 mol.% (190 °C, 195 min.) in the presence of monoclinic ZrO 2 .
... This catalyst has been shown to efficiently promote the direct transformation of LA into GVL using isopropyl alcohol (IPA) as a hydrogen donor. 27,28 The use of such one-pot systems would allow for avoiding the necessity of intermediate separation and purification downstream stages, potentially reducing the energy needs and capital costs. ...
... 5 At lab scale, we optimized the one-pot production of GVL from LA over Zr−Al−Beta catalyst, reaching high GVL yield and selectivity. 27,28 In a step forward in the transition of this process from research to industrial stage, herein we provide a techno-economic analysis to elucidate its feasibility as well as to identify the potential bottlenecks and process areas to be improved. ...
... In the reaction stage, LA is transformed into GVL in a single catalytic step in the presence of IPA as solvent and hydrogen donor (technical data for this reaction step are derived from our previous results on benchscale experiments). 27 The reaction block comprises a stirred batch reactor and the necessary auxiliary equipment, such as mixer, pump, and heater for the feedstock conditioning and product stream management. The reaction stage is followed by a purification and recovery stage to reach GVL commercialization specifications (99 wt % purity) and maximize the recovery of unreacted IPA for recycling. ...
Gamma-valerolactone (GVL) is a promising precursor for the preparation of biofuels and fuel-range hydrocarbons.
This work shows the conceptual design of a process for the
production of GVL from levulinic acid by means of catalytic
transfer hydrogenation (CTH) over a bifunctional Zr−Al−Beta
catalyst using an excess of isopropyl alcohol (IPA) acting as the
hydrogen donor and solvent. The process is advantageously
conducted in the liquid phase under moderate conditions, avoiding
the use of high-pressure hydrogen. A techno-economic analysis of
the process is presented, considering a production scale of 368.9
kg/h of GVL (ca. 85.5% GVL mass yield from levulinic acid). Such
an analysis considers two main process sections, namely, (i) the
reaction unit and (ii) the downstream purification section designed
to achieve 99 wt % GVL purity together with 95% recovery of
unreacted IPA. The analysis provides an investment of 6.4 MM€ with 7.5 MM€ annual operational costs (74% corresponding to
reactants). The Minimum Selling Price for GVL is estimated to be 3076 €/ton. Finally, cost sensitivity analyses revealed the high IPA
purchasing price and losses in side reactions (autoetherification) as the main obstacles to obtain a GVL competitive market price
through this approach.
... Therefore, the development of efficient strategies to transform these platform molecules is highly desirable for producing high-quality fuels and chemicals. On the industrial scale, several companies all over the world have developed industrial-scale processes for the production of levulinic acid and furfural, focusing on feasible commercial applications of levulinic acid, such as lactones, levulinate esters, aminolevulinic acid, or valeric biofuels [21,22]. ...
... In this field, our group has recently reported a family of Zr-Al-beta zeolites, synthesized via the post-synthetic modification of a dealuminated commercial beta zeolite. Such materials have been shown to be adequate catalysts for the direct and efficient production of GVL in isopropanol, not only from furfural and levulinic acid [22,50], but also from the corresponding parent monosaccharides, xylose [51,52] and glucose [53]. By tuning both the catalyst synthesis and the reaction conditions, these materials can be adapted to maximize the performance of the catalyst in terms of GVL yield and the efficient use of the respective biomass-derived substrate. ...
... GVL production in a lignocellulosic biorefinery producing both furfural (FAL) and levulinic acid (LA) is of great interest. Once the one-pot transformation has been successfully demonstrated in a batch-reactor configuration [22], the implementation of FAL and LA transformation in a continuous packed bed reactor holds an interest in order to scale the process up. The presented bifunctional Zr-Al-Beta catalyst harbors the key to such an efficient process. ...
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.
... where: ν (GVL) is the amount of moles of gamma-valerolactone formed, ν (Ru) is the amount of moles of ruthenium in the catalyst, t (reaction) is the reaction time equal to 0.25 h and the values of the catalyst productivity in relation to GVL (P GVL ), reflecting the ratio of the mass of GVL formed during the reaction (gGVL) to the mass of the loaded catalyst (gCat.) [11]: ...
... From the point of view of industrial application of the catalyst, the amount of the formed target product (GVL productivity) is no less important parameter than the molar yield of the product [11]. ...
Nanostructured 1 and 3% catalysts containing ruthenium nanoparticles supported on the initial and oxidized at different temperatures graphite-like carbon material Sibunit-4 prepared. A features of this support are mesoporous texture, hydrothermal stability and the presence of surface oxygen-containing functional groups responsible for the distribution of Ru nanoparticles and the catalyst acidic properties. The catalysts characterized using methods TEM, XPS, N2 adsorption, pHpzc and tested in the hydrogenation of levulinic acid to γ-valerolactone. It was found that the reaction rate and GVL selectivity are influenced by solvent choice, fractional composition, and acidic properties of the support. The obtained catalysts provide high activity in the reaction of direct hydrogenation of levulinic acid to γ-valerolactone (GVL yield 98 mol.%, At 160°С, 1.2 MPa H2) and high productivity (15.9 gGVL/gCat.). Obtained catalyst can be reused several times without noticeable loss of activity
... [18] Although a Zr MOF-808, containing Zr 6 oxoclusters, delivered 97 % GVL yield in a onepot cascade with sec-butanol at only 130°C, [19] activity was low requiring > 70 h. More promising are Zr-doped Al-Beta zeolites, for which Morales and co-workers obtained full LA conversion and 87 % GVL yield in batch with 2-propanol within 2 h reaction at 170°C; [20] the optimised productivity was 1.3 g GVL .g cat À 1 .h ...
Valerolactone (GVL) is a renewable and versatile platform chemical derived from sustainable carbon feedstocks. The cascade conversion of levulinic acid into GVL requires Brønsted and Lewis acid catalysed reactions. Here, a dual‐catalyst bed configuration is demonstrated that promotes synergy between Brønsted acid sites in sulfated zirconia (SZ) and Lewis acid sites in ZrO2/SBA‐15 for the liquid phase, continuous flow esterification and subsequent catalytic transfer hydrogenation (CTH) of levulinic acid to GVL. A saturated surface sulfate monolayer, possessing a high density of strong Brønsted acid sites, was optimal for levulinic acid esterification to isopropyl levulinate over SZ (>80 % conversion). A conformal ZrO2 bilayer, deposited over a SBA‐15 mesoporous silica and possessing mixed Brønsted:Lewis acidity, catalysed CTH of the levulinate ester and subsequent dealcoholisation/cyclisation to GVL (>60 % selectivity). Maximum stable productivity for the dual‐bed was 2.2 mmolGVL.gcat.h⁻¹ at 150 °C, significantly outperforming either catalyst alone or a physical mixture of both. Flow chemistry is a versatile approach to achieve spatial control over cascade transformations involving distinct catalytically active sites.
... Catalytic dehydration of hexoses or cellulose results in the formation of 5 HMF [4,6], and through hydration it can form LA [7]. On an industrial scale, several companies around the world have developed processes for the production of levulinic and furfural acid, focusing on viable commercial applications of levulinic acid, such as lactones, levulinate esters, or valeric biofuels [8,9]. Most of these processes involve GVL as an intermediary. ...
Valerolactone (GVL) has been considered an alternative as biofuel in the production of
carbon-based chemicals; however, the use of noble metals and corrosive solvents has been a prob�lem. In this work, Ni supported nanocatalysts were prepared to produce γ-Valerolactone from le�vulinic acid using methanol as solvent at a temperature of 170 °C utilizing 4 MPa of H2. Supports
were modified at pH 3 using acetic acid (CH3COOH) and pH 9 using ammonium hydroxide
(NH4OH) with different tungsten (W) loadings (1%, 3%, and 5%) by the Sol-gel method. Ni was
deposited by the suspension impregnation method. The catalysts were characterized by various
techniques including XRD, N2 physisorption, UV-Vis, SEM, TEM, XPS, H2-TPR, and Pyridine FTIR.
Based on the study of acidity and activity relation, Ni dispersion due to the Lewis acid sites contrib�uted by W at pH 9, producing nanoparticles smaller than 10 nm of Ni, and could be responsible for
the high esterification activity of levulinic acid (LA) to Methyl levulinate being more selective to
catalytic hydrogenation. Products and by-products were analyzed by 1H NMR. Optimum catalytic
activity was obtained with 5% W at pH 9, with 80% yield after 24 h of reaction. The higher catalytic
activity was attributed to the particle size and the amount of Lewis acid sites generated by modify�ing the pH of synthesis and the amount of W in the support due to the spillover effect.
... As shown in Scheme 1, the cascade transformation of LA to γ-GVL is composed of esterification, hydrogenation, and lactonization. 37,38 As the transfer hydrogenation of the carbonyl group is driven by Lewis acid, while esterification and lactonization are accelerated by Bro̷ nsted acid, a catalyst with both Lewis and Bro̷ nsted acidic sites is highly desired in the synthesis of γ-GVL. ...
Catalytic transformation of levulinic acid (LA) to γ-valerolactone (γ-GVL) is an important route for biomass upgradation. Because both Bro̷nsted and Lewis acidic sites are required in the cascade reaction, herein we fabricate a series of H3PW12O40@Zr-based metal-organic framework (HPW@MOF-808) by a facile impregnation method. The synthesized HPW@MOF-808 is active for the conversion of LA to γ-GVL using isopropanol as a hydrogen donor. Interestingly, with the increase in the HPW loading amount, the yield of γ-GVL increases first and then decreases, and 14%-HPW@MOF-808 gave the highest γ-GVL yield (86%). The excellent catalytic performance was ascribed to the synergistic effect between the accessible Lewis acidic Zr4+ sites in MOF-808 and Bro̷nsted acidic HPW sites. Based on the experimental results, a plausible reaction mechanism was proposed: the Zr4+ sites catalyze the transfer hydrogenation of carbonyl groups and the HPW clusters promote the esterification of LA with isopropanol and lactonization to afford γ-GVL. Moreover, HPW@MOF-808 is resistant to leaching and can be reused for five cycles without significant loss of its catalytic activity.
This review summarizes recent advances in the synthesis, characterization and application of heteroatom (Ti, Zr, Sn, and Hf) Lewis acid zeolites in the conversion of biomass-derived oxygenates.
We illustrate a sustainable and mild reaction process that efficiently transforms biomass‐derived furfural directly into GVL. Combining the homogeneous catalyst Ru‐MACHO‐BH with H3PO4(aq) allows to transform furfural to GVL in 84 % yield at 100 °C. This demonstrates the feasibility of transforming a major polysaccharide component in lignocellulose (hemicellulose) to GVL in a one‐pot direct approach without intermediate purification and isolation. image
High catalytic activity for selective and efficient transformation of levulinic acid (LA) to γ-valerolactone (GVL) in water was achieved over (η⁶-p-cymene)Ru(ii)-pyridylamine, [(η⁶-C10H14)RuCl(κ²-L)]⁺ (L = Namine-substituted pyridylamine ligands) based molecular catalysts. A series of complexes with pyridylamine ligands having different electronic and steric properties were synthesized and characterized. A significant influence of the Namine-substituents of the pyridylamine ligand on the catalytic activity was observed where the [(η⁶-p-cymene)RuCl(κ²-pyNHⁿpr)]⁺ catalyst ([Ru]-2) outperformed others with 87% yield and >99% selectivity for GVL at 80 °C in water. Advantageously, the activity of [Ru]-2 was also scaled up to gram scale transformation of LA to GVL. Control experiments, pH dependent NMR and mass studies revealed the involvement of crucial reaction intermediates and catalytic species in the transformation of LA to GVL.
Enabling large‐scale perovskite photovoltaic production requires understanding the integrated chemical process flow of precursor ink. Herein, a chemical process design is proposed for producing halide perovskite ink using biomass‐derived gamma‐valerolactone (GVL) as a green solvent for the first time. The proposed design has a perovskite ink production capacity of 154 kg h⁻¹ (at 1 m concentration), which is roughly equivalent to a peak power generation of 300 GW year⁻¹ from perovskite modules. Process simulations in ASPEN Plus showed that the reactor temperature, feedstock flow rate, and precursor colloidal size greatly impact the final ink quality. Under optimum conditions, 98.4% purity of GVL can be achieved through a catalyzed reaction between levulinic acid and isopropyl alcohol with acetone (99.98%) and water (99.99%) as by‐products. Providing a realistic chemical reaction scheme for halide perovskite ink formation as well as understanding the changes in its chemical properties over time are paramount to further improving the proposed process.
Pentenoic acids (PEA) obtained from biomass‐derived γ‐valerolactone (GVL) can serve as a platform for sustainable and atom‐economic synthesis of adipic acid and its derivatives. Herein, the results are reported on the cyclocarbonylation reaction of PEA to synthesize five‐ (5 a), six‐ (6 a), or seven‐membered (7 a) cyclic anhydrides, with the aim to drive the reaction towards 7 a, a potential intermediate to caprolactam. Carbonylation of 4‐PEA yielded up to 73 % cyclic anhydrides, 7 a and 6 a in ratio 79 : 21. However, from 3‐PEA the same palladium‐based catalytic system in the absence of strong acids yielded 61 % 6 a and 5 a (41 : 59), indicating the inability of the catalyst to force isomerization. Isomerization, which is essential to obtain 7 a from a mixture of PEA isomers derived from GVL, does occur in presence of strong acids; however, this led predominantly to formation of smaller rings (6 a and 5 a) from 4‐PEA. Catalytic systems containing ligands with bulky tert‐butyl substituents yielded 6 a and trace amounts of 7 a. Although 7 a can be obtained from 4‐PEA in reasonable selectivity, there still remains a challenge to selectively synthesize 7 a from a mixture of PEA isomers.
Levulinic acid (LA) is classified as a key platform chemical for biorefinery processes due to its wide potential applications and relatively low‐cost, as well as available technological routes from lignocellulose biomass. LA is an excellent precursor for the production of several industrially important products, such as γ‐valerolactone (GVL), 1,4‐pentanediol, 2‐methyl‐tetrahydrofuran, valeric acid, alkyl valerates, among others. Among the possible options for LA conversion into valuable products, catalytic hydrogenation has been considered one of the most important and is gaining increasing interest in recent years. GVL has been proposed as an illuminating liquid for burning coal without creating smoke or odor, also producing low volatile organic compounds emissions. Many studies indicated that homogeneous catalysts can give high yields of GVL under relatively mild and controllable reaction conditions.
Production of γ-valerolactone (GVL) from ethyl levulinate (EL) was studied by catalytic transfer hydrogenation (CTH) strategy under mild conditions. Hydrothermally synthesized Sn-Beta zeolites with high crystallinity show high catalytic activity and selectivity. With isopropanol as hydrogen source, 97.1 % GVL yield with 100 % selectivity was given under 110 °C. Crystallization time for synthesis of Sn-Beta showed great effect on the catalytic performance. Sn-Beta-xd catalysts with longer crystallization time (≥7 days) have high crystallinity and better catalytic performance. Firstly, longer crystallization time is necessary for the formation of large amount of Lewis acid sites which catalyze the conversion of EL to GVL. Secondly, high level of silanol groups in Sn-Beta has negative effect on the catalytic performance. High crystallinity means the amount of silanol groups in Sn-Beta-xd at a low level which is favorable for this CTH reaction. Meanwhile, this is why hydrothermally synthesized Sn-Beta shows higher catalytic activity than post-synthesized Sn-Beta in the conversion of EL to GVL. Furthermore, the catalyst was reusable.
The biomass-derived platform chemicals furfural and 5-(hydroxymethyl)furfural (HMF) may be converted to α-angelica lactone (AnL) and levulinic acid (LA). Presently, LA (synthesized from carbohydrates) has several multinational market players. Attractive biobased oxygenated fuel additives, solvents, etc., may be produced from AnL and LA via acid and reduction chemistry, namely alkyl levulinates and γ-valerolactone (GVL). In this work, hierarchical hafnium-containing multifunctional Linde type L (LTL) related zeotypes were prepared via top-down strategies, for the chemical valorization of LA, AnL and HMF via integrated catalytic transfer hydrogenation (CTH) and acid reactions in alcohol medium. This is the first report of CTH applications (in general) of LTL related materials. The influence of the post-synthesis treatments/conditions (desilication, dealumination, solid-state impregnation of Hf or Zr) on the material properties and catalytic performances was studied. AnL and LA were converted to 2-butyl levulinate (2BL) and GVL in high total yields of up to ca. 100%, at 200°C, and GVL/2BL molar ratios up to 10. HMF conversion gave mainly the furanic ethers 5-(sec-butoxymethyl)furfural and 2,5-bis(sec-butoxymethyl)furan (up to 63% total yield, in 2-butanol at 200°C/24 h). Mechanistic, reaction kinetics and material characterization studies indicated that the catalytic results depend on a complex interplay of different factors (material properties, type of substrate). The recovered-reused solids performed steadily.
The solvent-free production of diphenolic acid (DPA) from levulinic acid (LA) and phenol is studied using readily accessible commercial acid zeolites like Beta, ZSM-5 and USY. Acid zeolites are cost-effective catalysts, and they are herein benchmarked against the sulfonic acid resins Amberlyst-15 and Nafion®, and sulfonic acid-functionalized SBA-15 silicas. Beta zeolite with a moderate aluminum content (H-Beta 19, Si/Al=23) presents the best catalytic performance, owing to the right combination of the shape selectivity effect conferred by the BEA structure, and the adequate balance of acidity (Al content and speciation). The optimization of the reaction conditions is tackled by the response surface methodology using as optimization factors the temperature, the PhOH:LA molar ratio, and the catalyst loading. Thus, under the optimized reaction conditions (12 mmol LA, 140 ᵒC, 0.30 g catalyst loading, PhOH:LA = 6:1 mol), over 70% yield to DPA with LA conversion around 77% is obtained after 72 h. Despite the catalyst shows a progressive activity decay in successive uses because of fouling, removal of the formed organic deposits by calcination in air allows restoring the starting catalytic performance.
Biomass conversion to platform chemicals, value-added chemicals, or fuels is important because it provides a sustainable or carbon-neutral alternative to fossil fuel feedstocks. During the conversion of biomass into useful chemicals or fuels, the recalcitrant cell wall of the biomass feedstock is first broken down into useful sugars that can be converted over chemical catalysts or enzymes. Converting sugars to biofuels or useful chemicals over biological enzymes can be costly. Therefore, current research is more aligned with the employment of functionalized metal catalysts, which are preferred owing to their stability, recyclability, and easy separability. 2-Methyltetrahydrofuran (MTHF) is a vital sugar-derived platform chemical that is used as a green solvent, fuel additive, or as the starting material for synthesizing downstream chemicals such as dienes, pentane, and 2-pentanone. Based on MTHF formation from sugar derivatives and its further conversion over catalysts, this review discusses the challenges faced during the conversion of biomass to MTHF on precious and non-precious metal-based catalysts and the successive catalytic conversion of MTHF as a platform chemical to value-added downstream chemicals. Finally, the conclusions and perspectives for this catalytic biorefinery are proposed with future recommendations.
Selective hydrogenation of Levulinic acid (LA) to γ-Valerolactone (GVL) is an important reaction to produce high value-added chemicals and fuels but remains a big challenge. Herein we report a Ru/zeolite catalyst with Mn promotion, which exhibits excellent catalytic performance (yield: 98%) towards LA to GVL. The intrinsic activity (TOF) also increased obviously with the Mn addition. The particle size of Ru gradually decreased with the increase of Mn loading and a strong interaction between Ru and support was observed for the Ru-Mn/MCM-49 catalyst. The addition of Mn not only offered a good dispersion of Ru species on MCM-49, but also increased the L/B ratio of the catalyst, thereby contributing to the high GVL selectivity. High dispersed Ru sites were the intrinsic active sites of the catalyst verified by the in-situ experimental studies. The dissociation of the reactants was significantly enhanced, resulting in higher catalytic activity.
Acid treatment is the key to improve the physicochemical properties of metal-lignocellulosic hybrid, thus contributing to the catalytic performance for catalytic transfer hydrogenation (CTH) of carbonyl compounds to their corresponding alcohols. Herein, a series of organic acids were introduced to assist the design of Zr-Pennisetum sinese hybrid. Comprehensive studies demonstrated the dramatic changes of specific surface and acid/base sites of the prepared hybrid. Remarkably, formic acid-assisted [email protected]PS-FA possessed the largest surface area and enhanced interaction effects between acids (Lewis acid and Brønsted acid) and Lewis base sites, which exhibited excellent catalytic activity for CTH of levulinic acid to γ-valerolactone with a high yield of 95.6% in isopropanol under moderate reaction conditions (180 °C and 1.5 h). [email protected]PS-FA also showed remarkable cycle stability, and it could be consecutively used at least six runs without a significant loss in catalytic activity. More gratifyingly, [email protected]PS-FA displayed a superior universality for CTH of various carbonyl compounds to their corresponding alcohols, demonstrating great potential for upgrading biomass-derived aldehydes/ketones.
The production of jet-fuel precursors from the aldol-dimerization of levulinic acid (LA) over acid zeolites is presented. Under solventless conditions, high LA conversion with selectivities to LA dimers >90% are achieved. Chemisorption and spectroscopic analyses of the materials have revealed a cooperative effect between strong Brønsted (BS) and strong Lewis (LS) acid sites, which favors the selective formation of dimers. BEA structure is the most efficient owing to shape selectivity effect. H-Beta 19, having an optimum Brønsted to Lewis acid sites ratio and the adequate balance of BS/LS acid sites, displayed the best catalytic performance in terms of activity and selectivity to LA dimers. Under optimized reaction conditions H-Beta 19 achieved 79% LA conversion and >98% selectivity. An analysis on the stability showed good reusability in consecutive reaction cycles. The small loss of activity, ascribed to the formation of organic deposits, can be reverted by calcination in air.
Different renewable bio-based routes leading to the versatile bioproduct γ-valerolactone (GVL) were studied in integrated fashions, starting from furfural (Fur), α-angelica lactone (AnL) and levulinic acid (LA), in the presence of multifunctional hafnium-containing catalysts, in alcohol media. These routes involved acid and reduction reactions for which multifunctional catalysts were prepared via top-down strategies, namely the nanocatalyst Hf-deAlBeta-n and the hierarchical (intracrystalline micro/mesopores) microcrystalline material Hf-WdeSAlBeta-m. Mechanistic and kinetic modelling studies, molecular-level investigations by solid-state spectroscopic characterization, and catalyst stability studies led to assessments about the catalytic roles and potentialities of the prepared materials for GVL production. The influences of the catalytic reaction conditions and type of transition metal in the catalysts were studied. The best-performing catalyst was the hierarchical zeotype Hf-WdeSAlBeta-m (GVL yields of up to 99 % from LA, 91 % from AnL, and 73 % from Fur, at 180 °C), which correlated with its enhanced acidity and mesoporosity. To the best of our knowledge, this is the first reported hafnium-containing BEA zeotype possessing an intracrystalline hierarchical pore system, and the results highlighted the catalytic potentialities of these types of materials for the integrated production of GVL.
Levulinic acid (LA) is one of the most promising biomass derived platform chemicals owing to its wider convertibility to a large number of commodity chemicals. Numerous LA derivatives have paramount importance in the global economy. In this article, we have comprehensively reviewed various processes that have been developed to produce LA and its derivatives from different sugars and cellulosic feedstocks. These designs are discussed in order to provide comparative information on their chemical mechanism, process merits, demerits, and scale-up potentials. Monosacharides such as fructose, glucose and xylose and disaccharides such as sucrose are good feedstocks for LA production with Brønsted or Lewis acids as the catalysts in ether homogenous or heterogeneous reaction systems. LA yield is in the range of 2-90% which is greatly dependent on the reaction conditions. Polysaccharides such as cellulose and even lignocellulose are also employed for LA production. Brønsted acids especially mineral acids appear to be more efficient than Lewis acids to catalyze the conversion of polysaccharides and lignocellulosic biomass to LA. The important LA derivatives and their preparation reactions such as aminolevulinic acid, diphenolic acid, γ-valerolactone, various alkyl esters, valerate etc. also have been reviewed. These derivatives have extended utilization in modern industries due to the emergent environmental concerns. Furthermore, challenges arise out during these lab-scale processes are critically unveiled to pave the way for process selection and scale-up study for the production of LA and different derived chemicals. It has been recommended that to improve the efficiency of LA and its derivatives production, efforts should be made to develop robust catalysts and reaction system in order to improve the reaction selectivity. The mechanisms of LA formation from various feedstocks are also significantly important to guide the intensification of the process. Reactors with potential of industrial application are one of the crucial steps for scaling up of LA production.
γ-Valerolactone (GVL), which is a valuable chemical compound and a platform molecule, is considered as an intermediate product for the synthesis of chemical compounds with high added value, components of motor fuels and biopolymers. GVL is successfully used as an environmentally friendly solvent, fuel additive, fragrance and food additive. This review summarizes recent advances in the development of catalytic methods for the production of GVL from levulinic acid (LA), alkyl levulinates (AL), carbohydrates and vegetable polymers. Particular attention is paid to heterogeneous catalysts based on metals and metal oxides, which are more promising for practical application. The proposed mechanisms of processes are considered in detail, and prospects of using hydrogen-donor solvents in the production of GVL are discussed. Catalysts with the best catalytic performance were compared in terms of their productivity, which is an important parameter for industrial catalysis.
The present work is dedicated to the nickel phosphide based catalysts, containing particles, generated in situ in the reaction medium from the different catalytic systems. The present catalytic systems exhibited high activity in the hydroprocessing of furfural. Full conversion of furfural depending on conditions was reached after 0.5−3 hours of reaction at 250−350 °C. 2-methylfuran was obtained as a main product in toluene with the highest selectivity of 77 %. Ethyl levulinate and 2-methylfuran with selectivity of 40 % and 38 % respectively were obtained as main products in ethanol under different conditions. Different reaction medium and nickel phosphide precursors had an influence on the obtained phases of catalysts. Ni12P5 and Ni2P were obtained in toluene from oil-soluble precursors and Ni12P5 was obtained in ethanol from water-soluble precursors.
A method was developed for preparing bifunctional carbon Ni/NiO nanofiber catalysts that promotes efficient one-pot conversion of C5/C6 carbohydrates into levulinate esters in alcohol solvents. The bifunctional catalysts were prepared via solvothermal carbonization of 5-sulfosalicylic acid/NiSO4 without the use of sulfuric acid or hydrogen gas and had fine particle sizes (d= 5 nm to 50 nm) and contained -NH2, -SO3H, -COOH and phenolic -OH functional groups. Under optimal conditions, the catalysts afforded 93 % selectivity of ethyl levulinate in ethanol with major intermediate being 2-(ethoxymethyl)furan, 4,5,5-triethoxypentan-2-one and major byproducts being 2,5,5-triethoxpentan-2-one. Cooperative activity of Lewis acidity, Brønsted acidity and functional group sites of the catalyst is demonstrated for multi-step reaction sequences of C5/C6 carbohydrates with one-pot conversions and alcohols (methanol, ethanol, 1-propanol, 1-butanol) that act as both solvent and hydrogen donor source in which the bifunctional catalyst was shown to be five times recyclable with no apparent change in conversion and ca. 5 % change in selectivity.
Hydrogenolysis of alginic acid, derived from macroalgae, over Ru, Ni and Ru-Ni supported on activated carbon catalysts was performed in a batch reactor using NaOH, CaCO3, Ca(OH)2, and Mg(OH)2 as the basic promoters. Among the promoters used, NaOH provides the highest carbon efficiency and yield of glycols, such as ethylene glycol and 1,2-propanediol. In addition, various organic acids such as lactic acid, glycolic acid, and formic acid were produced in the form of salts. The hydrogenolysis of potential intermediates such as sorbitol, mannitol, lactic acid, and glycolic acid demonstrated direct conversion of alginic acid to glycols without sugar alcohols or organic acids as reaction intermediates. Furthermore, Ru-Ni bimetallic catalysts as a function of Ni/Ru molar ratio were used to increase the yield and selectivity of glycols. The highest yield of glycols, 24.1% was obtained when the Ni/Ru molar ratio was 1:1, due to the enhanced interaction between Ru and Ni based on H2-TPR.
The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) is an essential reaction step to produce value-added renewable chemicals and fuels. In this study, it is demonstrated that the dispersed state of metal and the acid properties of the support can be tuned directly in the synthesized stage for the Ru/MCM-49 catalysts. The average metal particle size of Ru was found at about 2.0 nm, and strong metal-support interaction was observed for the Ru/MCM-49(DP) catalyst. Mesopores presented can enhance the conversion rate for LA to GVL. The presence of a higher amount of Lewis acid sites can promote the ring closure esterification of the intermediate 4-HPA. High catalytic activity with a TOF value ˃3000 h-1, as well as excellent reusability, were achieved by Ru/MCM-49 (DP). The agglomeration of Ru particles and the coke formation was thought to be responsible for the deactivation of the catalyst.
Bifunctional catalysts have been considered to have vital importance in catalytic chemical process, but there is still some developing room for convenient materials with dual active sites. These catalysts have a notorious reputation for inhibiting mutual neutralization and controlling the distribution of active sites in order to perform their functions. We tailor a series of W-Zn-Al2O3 catalysts by modulating the doping density of metal species, which can boost the catalytic process of alcohols into corresponding carbonyl compounds in an additive-free-condition. Test results indicate that the proper content of zinc element can promote the overall activities, and subsequent adjustment of doping zinc can dramatically increase the electronic interaction and change the distribution of chemical active sites. Also, a plausible reaction mechanism was proposed to better understand the acid-base bifunctional catalytic process. Theoretical results confirm this system can provide certain references for similar reactants. Present reaction system is a green procedure and features a broad substrate scope, which reveals a sustainable method to process oxidative dehydrogenation reaction.
The direct one-pot transformation of glucose into γ-valerolactone (GVL) can be accomplished by means of a cascade of reactions in which Brønsted acid-catalyzed transformations are combined with catalytic transfer hydrogenation (CTH) by using 2-propanol as sacrificial alcohol, avoiding the use of high-pressure hydrogen. Catalysts containing Zr Lewis acid sites have been successfully applied in CTH reactions while the acid-driven transformations can be preferentially promoted by Brønsted Al-related acidity. Here, we present the combination of Zr and Al as active sites within a BEA zeolite structure as catalyst, with the possibility of adjusting the Al/Zr ratio from ∞ (commercial H-Beta) to 0 (aluminium-free Zr-Beta), which show a scale of Brønsted/Lewis acid sites ratios. The Al/Zr ratio has a strong impact on the products distribution. As the Zr content increases, higher amount of GVL is obtained, leading to a maximum over the catalyst with high amount of Zr and low content of Al acid sites (Al/Zr = 0.2). An increase of reaction temperature, as well as reaction time, allows an enhancement of yields towards the desired products, leading to a maximum yield towards GVL of 24 mol% over Zr-Al-Beta (2.0), and a maximum yield towards isopropyl lactate of 26 mol% over Zr-Beta at 190 °C.
γ-Valerolactone (GVL) is considered to be one of the most promising biomass platform compounds, and it can be synthesized using different reaction pathways from cellulose and hemicellulose, as well as their degradation derivatives. Based on the production of GVL and a preference for using whole biomass components, this paper comprehensively summarizes the catalytic system and reaction mechanism of each stage towards synthesizing sugar, levulinic acid, furfural (FAL) and GVL from the important biomass components cellulose and hemicellulose. The progress of each production process is analysed, and the research hotspots in the production stage are summarized. In particular, we compared the hydrogenation hydrolysis process of GVL using FAL and levulinic acid from cellulose and hemicellulose derivatives. In addition, this paper summarizes the application of the third largest component of lignin biomass in GVL production and proposes the synthesis of GVL by one-pot multi-step series reactions of cellulose and hemicellulose biomass.
Several Zr-based materials, including ZrO2 and Zr-SBA-15, with different silicon/zirconium molar ratios, and ZrO2/Si-SBA-15 (where SBA-15 stands for Santa Barbara Amorphous material no. 15), have been prepared as hydrogenation catalysts. The materials were characterized using different characterization techniques including X-ray diffraction (XRD), N2 porosimetry, scanning electron microscopy (SEM/EDX), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of pyridine adsorption and the pulsed chromatographic method using pyridine and 2,6-dimethylpyridine as probe molecules, mainly, have been employed for the characterization of the structural, textural, and acidic properties of the synthesized materials, respectively. The catalysts have been evaluated in the hydrogenation reaction of methyl levulinate using 2-propanol as hydrogen donor solvent. The reaction conditions were investigated and stablished at 30 bar system pressure with a reaction temperature of 200 °C using around 0.1 g of catalyst and a flow rate of 0.2 mL/min flow rate of a 0.3 M methyl levulinate solution in 2-propanol. All catalysts employed in this work exhibited good catalytic activities under the investigated conditions, with conversion values in the 15–89% range and, especially, selectivity to Υ-valerolactone in the range of 76–100% (after one hour time on stream). The highest methyl levulinate conversion and selectivity was achieved by ZrO2/Si-SBA-15 which can be explained by the higher dispersion of ZrO2 particles together with a highest accessibility of the Zr sites as compared with other materials such as Zr-SBA-15, also investigated in this work.
γ-valerolactone (GVL) is an important intermediate chemical with a wide range of applications as fuel, fuel additive and as a green solvent which has received a great deal of attentions from both academia and industry. This review aims to summarise the advances in conversion of renewable feedstocks into GVL through heterogeneous catalytic transfer hydrogenation (CTH) with a strong emphasis on discussing preparation, characterisation and performance of the catalysts in order to provide a better understanding of various catalytic systems and also to compare them in terms of catalytic performance. © 2017 Society of Chemical Industry.
Lignin is an abundant biopolymer with a high carbon content and high aromaticity. Despite its potential as a raw material for the fuel and chemical industries, lignin remains the most poorly utilised of the lignocellulosic biopolymers. Effective valorisation of lignin requires careful fine-tuning of multiple “upstream” (i.e., lignin bioengineering, lignin isolation and “early-stage catalytic conversion of lignin”) and “downstream” (i.e., lignin depolymerisation and upgrading) process stages, demanding input and understanding from a broad array of scientific disciplines. This review provides a “beginning-to-end” analysis of the recent advances reported in lignin valorisation. Particular emphasis is placed on the improved understanding of lignin's biosynthesis and structure, differences in structure and chemical bonding between native and technical lignins, emerging catalytic valorisation strategies, and the relationships between lignin structure and catalyst performance.
Zeolites containing Sn, Zr, Hf, Nb, or Ta heteroatoms are versatile catalysts for the activation and conversion of oxygenated molecules owing to the unique Lewis acid character of their tetrahedral metal sites. Through fluoride-mediated synthesis, hydrophobic Lewis acid zeolites can behave as water-tolerant catalysts, which has resulted in a recent surge of experimental and computational studies in the field of biomass conversion. However, many open questions still surround these materials, especially relating to the nature of their active sites. This lack of fundamental understanding is exemplified by the many dissonant results that have been described in recent literature reports. In this review, we use a molecular-based approach to provide insight into the relationship between the structure of the metal center and its reactivity toward different substrates, with the ultimate goal of providing a robust framework to understand the properties that have the strongest influence on catalytic performance for the conversion of oxygenates. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering Volume 7 is June 07, 2016. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
Increasing demand for sustainable chemicals and fuels has pushed academia and industry to search for alternative feedstocks replacing crude oil in traditional refineries. As a result, an immense academic attention has focused on the valorisation of biomass (components) and derived intermediates to generate valuable platform chemicals and fuels. Zeolite catalysis plays a distinct role in many of these biomass conversion routes. This contribution emphasizes the progress and potential in zeolite catalysed biomass conversions and relates these to concepts established in existing petrochemical processes. The application of zeolites, equipped with a variety of active sites, in Brønsted acid, Lewis acid, or multifunctional catalysed reactions is discussed and generalised to provide a comprehensive overview. In addition, the feedstock shift from crude oil to biomass involves new challenges in developing fields, like mesoporosity and pore interconnectivity of zeolites and stability of zeolites in liquid phase. Finally, the future challenges and perspectives of zeolites in the processing of biomass conversion are discussed.
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.
Neither the routes through which humin byproducts are formed, nor their molecular structure have yet been unequivocally established. A better understanding of the formation and physicochemical properties of humins, however, would aid in making biomass conversion processes more efficient. Here, an extensive multiple-technique-based study of the formation, molecular structure, and morphology of humins is presented as a function of sugar feed, the presence of additives (e.g., 1,2,4-trihydroxybenzene), and the applied processing conditions. Elemental analyses indicate that humins are formed through a dehydration pathway, with humin formation and levulinic acid yields strongly depending on the processing parameters. The addition of implied intermediates to the feedstocks showed that furan and phenol compounds formed during the acid-catalyzed dehydration of sugars are indeed included in the humin structure. IR spectra, sheared sum projections of solid-state 2DPASS (13) C NMR spectra, and pyrolysis GC-MS data indicate that humins consist of a furan-rich polymer network containing different oxygen functional groups. The structure is furthermore found to strongly depend on the type of feedstock. A model for the molecular structure of humins is proposed based on the data presented.
Levulinic acid (LA), easily derived from cellulose via acid catalytic process, is an attractive biomass-derived platform chemical, and can be converted into various valuable chemicals, which is an important content in biomass transformation. For LA conversion, non-noble metal catalytic systems have attracted significant attention due to their low cost compared with noble metals, and much progress has been achieved in recent years. This review focuses on efficient and selective transformation of LA into a diverse range of products in non-noble metal catalytic systems. A reasonable outlook is presented in the last part of the review to highlight the challenges and opportunities associated with LA upgrading over non-noble metal catalysts.
Controlling the thickness of zirconia monolayers coated over SBA-15 offers an effective way to tune catalytic performance for the acid-mediated and hydrogen transfer (Meerwein Ponndorf Verley, MPV) cascade transformation of furfural to γ-valerolactone. Complementary mechanistic and kinetic modelling establishes the existence of the two distinct zirconium active species (weak and strong acid sites), whose balancing enables optimisation of the cascade and hence maximal -valerolactone (GVL) production.
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.
Lignin, a major component of lignocellulose, is the largest source of aromatic building blocks on the planet and harbors great potential to serve as starting material for the production of biobased products. Despite the initial challenges associated with the robust and irregular structure of lignin, the valorization of this intriguing aromatic biopolymer has come a long way: recently, many creative strategies emerged that deliver defined products via catalytic or biocatalytic depolymerization in good yields. The purpose of this review is to provide insight into these novel approaches and the potential application of such emerging new structures for the synthesis of biobased polymers or pharmacologically active molecules. Existing strategies for functionalization or defunctionalization of lignin-based compounds are also summarized. Following the whole value chain from raw lignocellulose through depolymerization to application whenever possible, specific lignin-based compounds emerge that could be in the future considered as potential lignin-derived platform chemicals.
In pursuit of more sustainable and competitive biorefineries, the effective valorisation of lignin is key. An alluring opportunity is the exploitation of lignin as a resource for chemicals. Three technological biorefinery aspects will determine the realisation of a successful lignin-to-chemicals valorisation chain, namely (i) lignocellulose fractionation, (ii) lignin depolymerisation, and (iii) upgrading towards targeted chemicals. This review provides a summary and perspective of the extensive research that has been devoted to each of these three interconnected biorefinery aspects, ranging from industrially well-established techniques to the latest cutting edge innovations. To navigate the reader through the overwhelming collection of literature on each topic, distinct strategies/topics were delineated and summarised in comprehensive overview figures. Upon closer inspection, conceptual principles arise that rationalise the success of certain methodologies, and more importantly, can guide future research to further expand the portfolio of promising technologies. When targeting chemicals, a key objective during the fractionation and depolymerisation stage is to minimise lignin condensation (i.e. formation of resistive carbon–carbon linkages). During fractionation, this can be achieved by either (i) preserving the (native) lignin structure or (ii) by tolerating depolymerisation of the lignin polymer but preventing condensation through chemical quenching or physical removal of reactive intermediates. The latter strategy is also commonly applied in the lignin depolymerisation stage, while an alternative approach is to augment the relative rate of depolymerisation vs. condensation by enhancing the reactivity of the lignin structure towards depolymerisation. Finally, because depolymerised lignins often consist of a complex mixture of various compounds, upgrading of the raw product mixture through convergent transformations embodies a promising approach to decrease the complexity. This particular upgrading approach is termed funneling, and includes both chemocatalytic and biological strategies.
http://pubs.rsc.org/en/content/articlelanding/2018/cs/c7cs00566k#!divAbstract
We use infrared (IR) spectroscopy, gel permeation chromatography (GPC), and liquid chromatography-mass spectrometry (LC-MS) in multistage dissolution experiments in various solvents to investigate the solubility and molecular structure of humins formed during fructose dehydration. We demonstrate that the soluble fraction of humins correlates positively with the donor number of solvents resulting in significant dissolution at room temperature in solvents with high donor number. Most of the solubilized humins fragments have relatively low molecular weight (Mw), and the same species are present in different quantities as the residual solid is repeatedly dissolved in the same solvent. In contrast to the common belief of humins consisting of polymers of large Mw, we postulate for the first time that they are spatially and chemically heterogeneous and consist of insoluble macromolecules and small soluble species that are weakly associated within the structure. The solubility profiles of dissolved species in acetonitrile and methanol are different in terms of Mw but possess similar IR spectra, indicative of similar functional groups in dissolved species. Furthermore, we hypothesize that the identified humins fragments form through aldol condensation between 5-hydroxymethylfurfural and its hydrated products and through condensation of furanic species.
This article reviews the recent advances in the development of zeolite catalysts for biomass valorization processes to produce both biofuels and/or bio-based chemicals, which is an emerging and fast expanding field. The work deals with different types of feedstocks, including vegetable oils, lignocellulose and sugars, as well as with a number of relevant intermediates and platform molecules. Transformation of biomass into valuable products is hindered by a number of factors, mainly related to its complex composition, as biomass typically consists of bulky molecules with high oxygen content. Accordingly, biomass processing usually requires the combination of multiple steps and severe conditions, hence concepts like atom efficiency, product selectivity, and catalyst deactivation become of special relevance. A great progress has been achieved in the past years engineering the properties of zeolites for being adapted to the challenges associated to biomass valorization. The possibility of tailoring the main physicochemical properties of zeolites has become now a reality, being the major reason that explains the success achieved by this class of materials in a growing variety of biomass conversion pathways, as those described in this work: catalytic cracking and pyrolysis, hydrotreatments, with special relevance for hydrodeoxygenation processes, as well as in a high number of condensation, isomerization, and dehydration reactions. Thus, the development of hierarchical zeolites, exhibiting enhanced accessibility, and the possibility of introducing and combining in a controlled way different types of active sites (Brønsted and Lewis acid centers, basic sites, and metal phases) are the main basis of the excellent performance of zeolites in numerous biomass conversion routes.
The one-pot conversion of xylose into γ-gammavalerolactone in 2-propanol over bifunctional Zr-Al-Beta zeolites, prepared via a post-synthetic route, was optimized in terms of both catalyst synthesis and reaction conditions. In the catalyst preparation, the use of Zr(NO3)4 as zirconium source as well as the tuning of the amount of water used during the impregnation had a strong impact on the activity of the Zr species due to an improved dispersion of Zr species. As for the aluminium to zirconium exchange, an optimal Al/Zr ratio of 0.20 was identified to provide a catalyst with better activity. The modelization of the catalytic system through experimental design methodology allowed to identify the optimal values of the most influential reaction conditions: temperature 190 ºC, catalyst loading 15 g·L-1, and starting xylose concentration 30.5 g·L-1. Under these optimized reaction conditions, Zr-Al-Beta catalyst provides a GVL yield from xylose (ca. 34%) after only 10 h. The catalysts are stable and reusable after thermal regeneration at 550ºC.
Hierarchical Meso-Zr-Al-beta zeolites are successfully prepared through a multiple-step post-synthesis strategy composed of controlled dealumination, desilicication and metal incorporation. The presence of both Brønsted and Lewis acid sites with a certain extent of strength in Meso-Zr-Al-beta is demonstrated by NH3-TPD and FTIR spectroscopy with pyridine adsorption/desorption. The creation of mesopores via desilicication through alkaline treatment is confirmed by N2 adsorption/desorption isotherms. Meso-Zr-Al-beta, with Brønsted acid sites, Lewis acid sites and mesopores, is applied as a zeolite catalyst for the cascade conversion of biomass platform molecule furfural to γ-valerolactone. Owing to the presence of multiple functional sites and their mutual compatibility, remarkable activity for γ-valerolactone production and catalyst recyclability could be achieved with a single Meso-Zr-Al-beta, which appears to be a better catalyst than the commonly-employed combination catalyst systems. The multifunctional Meso-Zr-Al-beta zeolite is also applied as a promising catalyst in other cascade reactions in biomass valorization, i.e. glucose conversion to 5-hydromethylfurfural and trioses conversion to ethyl lactate. Similar zeolite catalysts containing multiple functional sites could be prepared via similar routes, and the number of acid sites and their strength can be adjusted to some extent to derive an optimized catalyst by changing the preparation parameters.
Innovative valorization of naturally abundant and renewable lignocellulosic biomass is of great importance in the pursuit of a sustainable future and biobased economy. Ionic liquids (ILs) as an important kind of green solvents and functional fluids have attracted significant attention for the catalytic transformation of lignocellulosic feedstocks into a diverse range of products. Taking advantage of some unique properties of ILs with different functions, the catalytic transformation processes can be carried out more efficiently and potentially with lower environmental impacts. Also, a new product portfolio may be derived from catalytic systems with ILs as media. This review focuses on the catalytic chemical conversion of lignocellulose and its primary ingredients (i.e., cellulose, hemicellulose, and lignin) into value-added chemicals and fuel products using ILs as the reaction media. An outlook is provided at the end of this review to highlight the challenges and opportunities associated with this interesting and important area.
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.
The sustainable conversion of biomass and biomass-derived platform chemicals demands efficient catalytic processes for which modified versions of zeolites can be strategically important. The catalytic potential of bulk and composite catalysts which simultaneously feature zeolite crystallinity, mesoporosity and Zr and Al sites were explored for the valorisation of furfural (Fur; industrially produced from hemicelluloses) via integrated reduction and acid reactions in alcohol media, to give useful bio-products (bioP), namely, furanic ethers, levulinate esters and angelica lactones. Different synthetic strategies were used starting from zeolite microcrystals or nanocrystals. A composite consisting of nanocrystals of Zr,Al-Beta embedded in a mesoporous matrix is reported for the first time. In a different synthesis approach, a bulk mesoporous zeotype material was prepared by post-synthesis alkaline/acid/impregnation treatments, and explored for the first time as a catalyst for a one-pot reduction/acid reaction system. Characterisation studies of the morphology, structure, texture and nature of the Al and Zr sites (²⁷Al MAS NMR spectroscopy, FT-IR spectroscopy of adsorbed pyridine or deuterated acetonitrile) helped understand the influence of material properties on catalytic performance. These types of materials are active and stable catalysts for the integrated conversion of Fur to bioP.
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.
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).
Reducing oxygen content in biomass-derived feedstocks via hydrodeoxygenation (HDO) is a key step in their upgrading to fuels and valuable chemicals. Organic molecules, e.g., alcohols and formic acid, can donate hydrogen to reduce the substrate in a process called catalytic transfer hydrogenation (CTH). Although practiced far less frequently than molecular hydrogen-based HDO processes, CTH has been proved to be an efficient and selective strategy in biomass upgrading in the last two decades. In this perspective article, we present a selective review of recent progress made in the upgrade of biomass-derived feedstocks through heterogeneous CTH, with a focus on the mechanistic interpretation. Hydrogenation and cleavage of C=O and C-O bonds, respectively, are the two main categories of reactions discussed, owing to their importance in the HDO of biomass-derived feedstocks. On acid/base catalysts, Lewis acid-base pair sites, rather than a single acid or base site, mediate hydrogenation of carbonyl groups with alcohols as the hydrogen donor. While acid/base catalysts typically only catalyze the hydrogenation of carbonyl groups with alcohols as the hydrogen donor, metal-based catalysts are able to mediate both hydrogenation and hydrogenolysis reactions with either alcohols or formic acid. Several model reactions involving platform chemicals in biomass upgrading, e.g., 5-hydroxymethylfurfural, levulinic acid and glycerol, are used in the discussion to illustrate general trends. Because alcohols are typically both the hydrogen donor and the solvent, the donor and solvent effects are intertwined. Therefore, solvent effects are discussed primarily in the context of sugar isomerization and reactions with formic acid as the hydrogen donor, in which the solvent and hydrogen donor are two separate species. Current challenges and opportunities of future research to develop CTH into a competitive and complimentary strategy of the conventional molecular hydrogen-based processes are also discussed.
Hydrogenation of levulinic acid (LA) was investigated with several supported Ni catalysts for the production of γ-valerolactone (GVL). The catalysts have been characterized with different techniques (XRD, N2 adsorption-desorption, TPR, ICP-AES, TEM). Under optimal reaction conditions of 150 °C, 1.0 MPa and 20 mL i-PrOH for 2 h, the highest selectivity (93.3%) of GVL was obtained. The productivity reached 0.32 mol(GVL) g(metal)(-1) h(-1), which was highest compared with all reported Ni-based catalysts.
The carbohydrates (cellulose, starch, inulin, maltose, sucrose, glucose and fructose) were converted efficiently into γ-valerolactone (GVL) over combined H3PW12O40 and Ru/TiO2 catalysts under mild conditions. The basicity of oxygen-containing solvents had a remarkable effect on the acid strength of H3PW12O40, which resulted in a great variation in the yield of GVL. H3PW12O40 was more effective in 20 vol% water/γ-butyrolactone than in pure water and other water/organic solvents (methanol, ethanol and 1,4-dioxane). GVL yields for inulin and fructose reached 70.5 mol% and 67.6 mol% respectively. Meanwhile, a GVL yield of 40.5 mol% was achieved for cellulose. Besides, a practical method for catalyst recycling and GVL separation was developed by adding sugar into the reaction mixture. H3PW12O40 and Ru/TiO2 maintained its activity after three recycling runs.
Hydroxymethylfurfural (HMF) and levulinic acid (LA) are two of the most promising chemicals derived from biomass owing to their convertibility into a large number of chemicals having applications in diverse industries. Their transition from niche products to mass-produced chemicals, however, requires their production from sustainable biomass feedstocks at low costs using environment-friendly techniques. In this review, the numerous reaction systems that have been developed to produce HMF and LA from various substrates have been looked at and their merits, demerits and requirements for commercialisation outlined. Special attention has been paid to microwave irradiation-heated systems due to their dual advantages of high product yields and low environmental footprint.
Levulinic acid (LA), 4-oxo-pentanoic acid, is a new platform chem. with various potential uses. In this paper, catalytic hydrogenation and oxidn. of levulinic acid were studied. It was shown from expts. that levulinic acid can be hydrogenated to γ-valerolactone (GVL) over transition metal catalysts and oxidative-decarboxylated to 2-butanone (methyl-ethyl-ketone, MEK) and methyl-vinyl-ketone (MVK) by cupric oxide (CuO), cupric oxide/cerium oxide (CuO/CeO2), cupric oxide/alumina (CuO/Al2O3), and silver(I)/peroxydisulfate (Ag(I)/S2O82-). [on SciFinder(R)]
Natural molecular biomass plays an important role in the field of renewable polymers, as they can be directly used or derivatized as monomers for controlled polymerization, in a way similar to many petroleum-derived monomers. We deliver this perspective primarily based on a monomer approach. Biomass-derived monomers are separated into four major categories according to their natural resource origins: (1) oxygen-rich monomers including carboxylic acids (lactic acid, succinic acid, itaconic acid, and levulinic acid) and furan; (2) hydrocarbon-rich monomers including vegetable oils, fatty acids, terpenes, terpenoids and resin acids; (3) hydrocarbon monomers (bio-olefins); and (4) non-hydrocarbon monomers (carbon dioxide). A variety of emerging synthetic tools (controlled polymerization and click chemistry) are particularly summarized. An overview on future opportunities and challenges, which are critical to promote biorefinery in the production of renewable chemicals and polymers, is given.
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.
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.
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.
The acid-catalyzed conversion of 5-hydroxymethylfurfural (HMF) produces levulinic and formic acids in equal amounts. Dark-colored solids, known as humins, are also formed in a parallel reaction. Aldol addition and condensation are proposed as important reactions in the acid-catalyzed growth of humins, adding HMF to 2,5-dioxo-6-hydroxy-hexanal. Consistent with this proposal, infrared (IR) spectra of humins formed from HMF indicate that the furan ring and hydroxymethyl group of HMF are present in the humins, but the carbonyl group is not. Similarly, if a mixture of HMF and benzaldehyde are processed, IR spectra of the humins indicate the additional presence of the aromatic ring from benzaldehyde but not its carbonyl group. The incorporation of the aromatic ring from benzaldehyde in the humins demonstrates the possibility of functionalizing humins to increase their value.
Efficient synthesis of renewable fuels remains a challenging and important line of research. We report a strategy by which
aqueous solutions of γ-valerolactone (GVL), produced from biomass-derived carbohydrates, can be converted to liquid alkenes
in the molecular weight range appropriate for transportation fuels by an integrated catalytic system that does not require
an external source of hydrogen. The GVL feed undergoes decarboxylation at elevated pressures (e.g., 36 bar) over a silica/alumina
catalyst to produce a gas stream composed of equimolar amounts of butene and carbon dioxide. This stream is fed directly to
an oligomerization reactor containing an acid catalyst (e.g., H ZSM-5, Amberlyst-70), which couples butene monomers to form
condensable alkenes with molecular weights that can be targeted for gasoline and/or jet fuel applications. The effluent gaseous
stream of CO2 at elevated pressure can potentially be captured and then treated or sequestered to mitigate greenhouse gas emissions from
the process.
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Studies were carried out on the effects of temperature, acid concentration, liquid:solid ratio and reaction time on levulinic acid production from wheat straw using response surface methodology. The P-value of the coefficient for acid concentration was 0.0002, suggesting that this was highly significant. The quadratic effects of temperature and liquid:solid ratio were also significant and their P-values were <0.0001 and 0.0027, respectively. The coefficient determination (R(2)) was good for the second-order model. The optimal conditions for levulinic acid production from wheat straw were 209.3 degrees C, 3.5% acid concentration, 15.6 liquid:solid ratio and 37.6 min of reaction time resulted 19.86% yield.