Cascade strategy for the tunable catalytic valorization of levulinic acid and γ-valerolactone to 2-methyltetrahydrofuran and alcohols

A cascade strategy for the catalytic valorization of aqueous solutions of levulinic acid as well as of γ-valerolactone to 2-methyltetrahydrofuran or to monoalcohols, 2-butanol and 2-pentanol, has been studied and optimized. Only commercial catalytic systems have been employed, adopting sustainable reaction conditions. For the first time, the combined use of ruthenium and rhenium catalysts supported on carbon, with niobium phosphate as acid co-catalyst, has been claimed for the hydrogenation of γ-valerolactone and levulinic acid, addressing the selectivity to 2-methyltetrahydrofuran. On the other hand, the use of zeolite HY with commercial Ru/C catalyst favors the selective production of 2-butanol, starting again from γ-valerolactone and levulinic acid, with selectivities up to 80 and 70 mol %, respectively. Both levulinic acid and γ-valerolactone hydrogenation reactions have been optimized, investigating the effect of the main reaction parameters, to properly tune the catalytic performances towards the desired products. The proper choice of both the catalytic system and the reaction conditions can smartly switch the process towards the selective production of 2-methyltetrahydrofuran or monoalcohols. The catalytic system [Ru/C + zeolite HY] at 200 °C and 3 MPa H2is able to completely convert both γ-valerolactone and levulinic acid, with overall yields to monoalcohols of 100 mol % and 88.8 mol %, respectively

Integrated Cascade Process for the Catalytic Conversion of 5-Hydroxymethylfurfural to Furanic and Tetrahydrofuranic Diethers as Potential Biofuels

The depletion of fossil resources is driving the research towards alternative renewable ones. Under this perspective, 5-hydroxymethylfurfural (HMF) represents a key molecule deriving from biomass characterized by remarkable potential as platform chemical. In this work, for the first time, the hydrogenation of HMF in ethanol was selectively addressed towards 2,5-bis(hydroxymethyl)furan (BHMF) or 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) by properly tuning the reaction conditions in the presence of the same commercial catalyst (Ru/C), reaching the highest yields of 80 and 93 mol%, respectively. These diols represent not only interesting monomers but strategic precursors for two scarcely investigated ethoxylated biofuels, 2,5-bis(ethoxymethyl)furan (BEMF) and 2,5-bis(ethoxymethyl)tetrahydrofuran (BEMTHF). Therefore, the etherification with ethanol of pure BHMF and BHMTHF and of crude BHMF, as obtained from hydrogenation step, substrates scarcely investigated in the literature, was performed with several commercial heterogeneous acid catalysts. Among them, the zeolite HZSM-5 (Si/Al=25) was the most promising system, achieving the highest BEMF yield of 74 mol%. In particular, for the first time, the synthesis of the fully hydrogenated diether BEMTHF was thoroughly studied, and a novel cascade process for the tailored conversion of HMF to the diethyl ethers BEMF and BEMTHF was proposed

New Frontiers in the Catalytic Synthesis of Levulinic Acid: From Sugars to Raw and Waste Biomass as Starting Feedstock

Levulinic acid (LA) is one of the top bio-based platform molecules that can be converted into many valuable chemicals. It can be produced by acid catalysis from renewable resources, such as sugars, lignocellulosic biomass and waste materials, attractive candidates due to their abundance and environmentally benign nature. The LA transition from niche product to mass-produced chemical, however, requires its production from sustainable biomass feedstocks at low costs, adopting environment-friendly techniques. This review is an up-to-date discussion of the literature on the several catalytic systems that have been developed to produce LA from the different substrates. Special attention has been paid to the recent advancements on starting materials, moving from simple sugars to raw and waste biomasses. This aspect is of paramount importance from a sustainability point of view, transforming wastes needing to be disposed into starting materials for value-added products. This review also discusses the strategies to exploit the solid residues always obtained in the LA production processes, in order to attain a circular economy approac

Novel Challenges on the Catalytic Synthesis of 5-Hydroxymethylfurfural (HMF) from Real Feedstocks

The depletion of fossil resources makes the transition towards renewable ones more urgent. For this purpose, the synthesis of strategic platform-chemicals, such as 5-hydroxymethylfurfural (HMF), represents a fundamental challenge for the development of a feasible bio-refinery. HMF perfectly deals with this necessity, because it can be obtained from the hexose fraction of biomass. Thanks to its high reactivity, it can be exploited for the synthesis of renewable monomers, solvents, and bio-fuels. Sustainable HMFsynthesis requires the use of waste biomasses, rather than model compounds such as monosaccharides or polysaccharides, making its production more economically advantageous from an industrial perspective. However, the production of HMF from real feedstocks generally suffers from scarce selectivity, due to their complex chemical composition and HMF instability. On this basis, different strategies have been adopted to maximize the HMF yield. Under this perspective, the properties of the catalytic system, as well as the choice of a suitable solvent and the addition of an eventual pretreatment of the biomass, represent key aspects of the optimization of HMF synthesis. On this basis, the present review summarizes and critically discusses the most recent and attractive strategies for HMF production from real feedstocks, focusing on the smartest catalytic systems and the overall sustainability of the adopted reaction conditions

Tunable and selective hydrogenation of HMF to furan diols in flow reactor using Ru/C

5-hydroxymethylfurfural (HMF) is a key renewable platform-chemical and precursor of several valuable products. In particular, 2,5-bis(hydroxymethyl)furan (BHMF) and 2,5- bis(hydroxymethyl)tetrahydrofuran (BHMTHF) are very important monomers for the synthesis of bio- polymers and precursors of other relevant monomers, such as caprolactame and 1,6-hexanediol. BHMF and BHMTHF derive from the hydrogenation of the aldehydic group and also of the furanic ring of HMF, respectively. The two steps are catalysed by noble metals and Ru/C has already resulted particularly active and selective for the synthesis of each diol performing the reaction in batch in water medium. However, for industrial application the employment of a flow reactor set-up is more suitable because it allows a continuous production and improves the energy efficiency, mixing control and heat transfer. The employment of the flow reactor is fundamental in particular for three phase reactions, as the hydrogenation of HMF. In fact, it allows the increase of the interfacial area between the phases, leading to more efficient heat and mass transfers. Although the advantages of the flow reactor, only recently in the literature it has been used for the HMF hydrogenation to BHMF and BHMTHF. The reaction has been generally carried out in organic solvents, in the presence of ad hoc synthesised catalysts, producing only one of the two diols. In this context, the present work proposes, for the first time, the optimization of the selective synthesis of each diol, BHMF and BHMTHF, starting from pure aqueous HMF solution in the flow reactor employing the same commercial catalyst (5 wt% Ru/C), by simply tuning the reaction parameters

Cascade Valorization of 5-Hydroxymethylfurfural (HMF) to Monomers and Furanic/Tetrahydrofuranic Diethers Bio-fuels

5-hydroxymethylfurfural (HMF) represents a valuable platform-chemical for the synthesis of monomers and bio-fuels. Thus, the present work proposes, for the first time, a cascade process for the synthesis of diol monomers and furanic/tetrahydrofuranic diethers as novel bio-fuels starting from HMF. In the first step, the selective hydrogenation of HMF in ethanol to give 2,5- bis(hydroxymethyl)furan (BHMF) or 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) was carried out by properly tuning the reaction conditions in the presence of 5 wt% Ru/C as catalyst, reaching the highest yields of 80 and 93 mol%, respectively. These diols are strategic precursors for two scarcely investigated ethoxylated bio-fuels, 2,5-bis(ethoxymethyl)furan (BEMF) and 2,5- bis(ethoxymethyl)tetrahydrofuran (BEMTHF). Thus, in the second step, the etherification of both pure BHMF and BHMTHF to give BEMF and BEMTHF, respectively, was studied. The zeolite HZSM-5 (Si/Al = 25) allowed the achievement of the highest BEMF yield of 74 mol%. Analogous results were also obtained starting from crude BHMF. On the contrary, BEMTHF was not obtained by the direct etherification of BHMTHF, but a preliminary study showed the possibility of synthesising BEMTHF by the 5 wt% Ru/C catalyzed hydrogenation of BEMF. Finally, the stability of the tested catalysts was investigated, showing that they maintained the activity almost constant up to five recycle runs, thus resulting recyclable

Smart valorization of waste biomass: Exhausted lemon peels, coffee silverskins and paper wastes for the production of levulinic acid

In recent years, the replacement of fossil resources with renewable ones has focused great interest, expecially as regards the production of new valuable bio-products and bio-fuels, in progressive replacement of the traditional petroleum-based ones.The Waste Management Policy strongly encourages the valorization of waste biomasses into added-value bio-chemicals, instead of their traditional combustion for energy recovery or, even worse, of their landfill disposal. In this context, the acid-catalysed hydrothermal conversion of negative-value bio-wastes into levulinic acid (LA) represents a smart exploitation possibility, already developed and optimized on pilot-scale, and widely adaptable to different kinds of feedstocks. In this work, the LA production was investigated starting from two bio-wastes deriving from industrial Italian food-processing, e.g.exhausted lemon peels and coffee silverskins, together with that of a clean cellulose powder, which derives from the cutting operations occurring during the tissue paper production. The effect of the main reaction parameters on the LA synthesis, in particular the concentration of the acid catalyst, the biomass loading, the reaction temperature/time and, additionally, the effect of an upstream milder acid pretreatment, was investigated and discussed. Moreover, in the case of coffee silverskin, a preliminary extraction step of the water-soluble phenolics has further improved the fractionation and exploitation of this waste biomass. These compounds have been proposed as natural antioxidants, which represent very valuable niche products for nutraceutical uses. The described examples confirm the feasibility of an integrated valorization of the waste biomass, well in agreement with the Biorefinery concept

Tunable HMF hydrogenation to furan diols in a flow reactor using Ru/C as catalyst

5-hydroxymethylfurfural (HMF), accessible from various feedstocks, represents an important renewable platform-chemical, precursor for valuable biofuels and bio-based chemicals. In this work, the continuous hydrogenation of an aqueous solution of HMF to give strategic monomers, 2,5-bis(hydroxymethyl)furan (BHMF) and 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) was investigated in a continuous flow reactor adopting a commercial Ru/C (5 wt%) as catalyst. The influence of the main process variables on products yield and selectivity was studied and optimized. The highest BHMF and BHMTHF yields of 87.9 and 93.7 mol%, respectively, were achieved by tuning the catalyst contact time, keeping all other variables constant (temperature, pressure, hydrogen flow rate, initial HMF concentration). Intraparticle diffusion limitation for hydrogen and HMF was shown to occur at some of the tested conditions by performing the HMF hydrogenation with different catalyst particle sizes, confirmed by calculations. Constant catalyst activity was observed up to 6 h time-on-stream and then gradually reduced. Fresh and spent catalyst characterization showed no significant sintering and negligible leaching of ruthenium during time-on-stream. A decrease of the specific surface area was observed, mainly due to humin deposition which is likely the reason for catalyst deactivation. Catalyst performance could be restored to initial values by a thorough washing of the catalyst.</p

Tunable HMF hydrogenation to furan diols in a flow reactor using Ru/C as catalyst

5-hydroxymethylfurfural (HMF), accessible from various feedstocks, represents an important renewable platform-chemical, precursor for valuable biofuels and bio-based chemicals. In this work, the continuous hydrogenation of an aqueous solution of HMF to give strategic monomers, 2,5-bis(hydroxymethyl)furan (BHMF) and 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) was investigated in a continuous flow reactor adopting a commercial Ru/C (5 wt%) as catalyst. The influence of the main process variables on products yield and selectivity was studied and optimized. The highest BHMF and BHMTHF yields of 87.9 and 93.7 mol%, respectively, were achieved by tuning the catalyst contact time, keeping all other variables constant (temperature, pressure, hydrogen flow rate, initial HMF concentration). Intraparticle diffusion limitation for hydrogen and HMF was shown to occur at some of the tested conditions by performing the HMF hydrogenation with different catalyst particle sizes, confirmed by calculations. Constant catalyst activity was observed up to 6 h time-on-stream and then gradually reduced. Fresh and spent catalyst characterization showed no significant sintering and negligible leaching of ruthenium during time-on-stream. A decrease of the specific surface area was observed, mainly due to humin deposition which is likely the reason for catalyst deactivation. Catalyst performance could be restored to initial values by a thorough washing of the catalyst

Sustainable Valorisation and Efficient Downstream Processing of Giant Reed by High-Pressure Carbon Dioxide Pretreatment

This work investigated the catalytic high-pressure CO2 pretreatment of giant reed. CO2 is a renewable resource; its use does not generate chemical wastes and it can be easily removed and recycled. The effect of the addition of low concentrations of FeCl3 (0.16 wt%) and PEG 400 (1.0 wt%) on the hemicellulose hydrolysis to xylose and xylo-oligosaccharides (XOS) is reported for the first time. Under the optimised pretreatment conditions, the xylan conversion of 82 mol% and xylose and XOS yields of 43 and 20 mol% were achieved, respectively. The solid residues obtained from different pretreatments were used as the substrate for the enzymatic hydrolysis to give glucose. The total glucose yield achieved under the optimised two-step process was 67.8 mol% with respect to the glucan units in the biomass. The results demonstrated that PEG-assisted FeCl3-catalysed scCO(2) pretreatment can produce xylose- or XOS-rich hydrolysates and improve the enzymatic hydrolysis of biomass