The Perspective of Using the System Ethanol-Ethyl Acetate in a Liquid Organic Hydrogen Carrier (LOHC) Cycle

Starting from bioethanol it is possible, by using an appropriate catalyst, to produce ethyl acetate in a single reaction step and pure hydrogen as a by-product. Two molecules of hydrogen can be obtained for each molecule of ethyl acetate produced. The mentioned reaction is reversible, therefore, it is possible to hydrogenate ethyl acetate to reobtain ethanol, so closing the chemical cycle of a Liquid Organic Hydrogen Carrier (LOHC) process. In other words, bioethanol can be conveniently used as a hydrogen carrier. Many papers have been published in the literature dealing with both the ethanol dehydrogenation and the ethyl acetate hydrogenation to ethanol so demonstrating the feasibility of this process. In this review all the aspects of the entire LOHC cycle are considered and discussed. We examined in particular: the most convenient catalysts for the two main reactions, the best operative conditions, the kinetics of all the reactions involved in the process, the scaling up of both ethanol dehydrogenation and ethyl acetate hydrogenation from the laboratory to industrial plant, the techno-economic aspects of the process and the perspective for improvements. In particular, the use of bioethanol in a LOHC process has three main advantages: (1) the hydrogen carrier is a renewable resource; (2) ethanol and ethyl acetate are both green products benign for both the environment and human safety; (3) the processes of hydrogenation and dehydrogenation occur in relatively mild operative conditions of temperature and pressure and with high energetic efficiency. The main disadvantage with respect to other more conventional LOHC systems is the relatively low hydrogen storage density

PIXE mapping on multiphase fluid inclusions in endoskarn xenoliths of AD 472 eruption of Vesuvius (Italy)

In this work we report a microthermometric and proton-induced X-ray emission (PIXE) mapping investigation on multiphase fluid inclusions hosted within nepheline and clinopyroxene of endoskarn xenoliths present in the deposits of the AD 472 eruption of Vesuvius. PIXE mapping on magmatic fluid inclusions repesents a useful tool for the characterization of the composition of magma derived fluids, exsolved from active magma chambers. In fluid inclusions we observed the occurrence of widespread solid phases formed by Fe, Pb, Zn, As ± Cu ± Mn, suggesting the good metal transport capability of Vesuvius magmatic fluids, which interacted with carbonate country rocks leading to the formation of endoskarn

Integrated Cascade Process for the Catalytic Conversion of 5-Hydroxymethylfurfural to Furanic and TetrahydrofuranicDiethers 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

Insights on butyl levulinate bio-blendstock: From model sugars to paper mill waste cellulose as feedstocks for a sustainable catalytic butanolysis process

Butyl levulinate (BL) represents a novel diesel bio-blendstock and a versatile intermediate and solvent. The onepot acid-catalyzed conversion of C6-feedstocks, employing n-butanol as the solvent/reagent, implies the upgrading of low-cost or, even better, waste biomasses for developing prompt process intensification. In this paper, the one-pot butanolysis process has been studied, moving from model glucose and microcrystalline cellulose to a waste cellulose feedstock deriving from a real papermaking process. The performances obtained with this waste biomass have been optimized, achieving BL yields up to 46 mol %, adopting a high-gravity approach, in the presence of diluted sulfuric acid as the catalyst. The optimization was carried out also in the perspective of minimizing the alcohol etherification to dibutyl ether, and the feedstock carbonization to char by-product, whose characterization was performed to identify its suitable applications. The combined production of both BL as a valuable bio-fuel and char as an exploitable carbonaceous bio-material can pave the way to the development of the one-pot butanolysis of real cellulosic or lignocellulosic biomasses in an environmentally sustainable and integrated perspective, in agreement with the principles of the circular bio-economy

Synthesis of 1-Hexanol/Hexyl hexanoate Mixtures from Grape Pomace: Insights on Diesel Engine Performances at High Bio-Blendstock Loadings

The production of oxygenated bio-additives for traditional fuels represents a key challenge due to their depletion in the near-future and their positive contribution to the reduction in environmental pollution. The present study considers the synthesis of 1-hexanol/hexyl hexanoate mixtures, two oxygenated Diesel bio-additives produced through the hydrogenation of hexanoic acid, obtainable from the fermentation of a wide variety of waste biomasses. In our case, crude hexanoic acid was produced through the fermentation of grape pomace, an abundant Italian agrifood waste. Commercial 5 wt% Re/γ-Al2O3 was adopted for the catalytic hydrogenation of crude hexanoic acid, and the support acidity allowed the tuning of the reaction selectivity toward the formation of hexyl hexanoate, instead of 1-hexanol, reaching yields of 40 and 25 mol%, respectively. The effects of each bio-additive on Diesel engine performance and exhaust emissions (soot, nitrogen oxides, carbon monoxide, unburned hydrocarbons) were evaluated, highlighting noteworthy positive effects especially on the reduction in carbon monoxide and soot emissions, if compared with those of Diesel fuel alone. Similar promising performances were achieved by employing Diesel blend mixtures of 1-hexanol/hexyl hexanoate, mimicking typical compositions of the rhenium-catalyzed post-hydrogenation mixtures. Even in such cases, 1-hexanol/hexyl hexanoate mixtures can be blended with commercial Diesel fuel, up to high loadings currently not yet investigated (20 vol%), without altering the engine performances and, again, significantly lowering soot and carbon monoxide emissions by more than 40%. This work highlights the possibility of obtaining such oxygenated bio-additives starting from waste through to a fully sustainable process and proves their beneficial effects on the reduction in exhaust emissions with no changes in engine performance

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

Biomass-derived catalysts: synthesis and characterization of hydrochars and pyrochars

Lignocellulosic biomass is one of the more important renewable sources and it will play a strategic role in many future markets, taking into consideration that a renewable energy share of 32% is binding at the European level by 2030. Deconstruction of lignocellulosic biomass can be carried out via hydrothermal processes and, among them, hydrothermal carbonization (HTC) represents a versatile process, which promotes the progressively deoxygenation of the biomass, under relatively mild reaction conditions. The obtained solid-rich product, called hydrochar, can be used in a wide range of applications, such as adsorption, energy storage, CO2 sequestration, catalysis etc. In this last field, within the project PRIN 2020 LEVANTE “LEvulinic acid Valorization through Advanced Novel Technologies” (2020CZCJN7), different hydrochars have been synthesized starting from cellulose and the effects of the main reaction parameters have been investigated employing statistical modelling. Under the selected set of processing parameters, the yield of hydrochars was in the range 38-48 wt%, with a carbon content of 60-70 wt% and corresponding higher heating values amounting to 17-27 MJ/kg, confirming the successful conversion of cellulose into a carbonaceous material. Finally, on the basis of final applications, also pyrochars have been prepared starting from the optimal hydrochars, in order to increase the aromatization degree and the surface areas. All the synthesized hydrochars and pyrochars will be further functionalized and employed, as acid catalysts, for the valorization of levulinic acid, in particular for its conversion to diphenolic acid, in agreement with the objectives of the project LEVANTE

Conversion of the hydrochar recovered after levulinic acid production into activated carbon adsorbents

Levulinic acid production by acid-catalyzed hydrothermal conversion of (ligno)cellulosic biomass generates significant amounts of carbonaceous hydrochar, which is currently considered a final waste. In this work, the hydrochar recovered after the levulinic acid production, was subjected to cascade pyrolysis and chemical activation treatments (by H3PO4 or KOH), to synthesize activated carbons. The pyrolysis post-treatment was already effective in improving the surface properties of the raw hydrochar (Specific Surface Area: 388 m2/g, VP: 0.22 cm3/g, VMESO: 0.07 cm3/g, VMICRO: 0.14 cm3/g), by removing volatile compounds. KOH activation resulted as the most appropriate for further improving the surface properties of the pyrolyzed hydrochar, showing the best surface properties (Specific Surface Area: 1421 m2/g, VP: 0.63 cm3/g, VMESO: 0.10 cm3/g, VMICRO: 0.52 cm3/g), which synergistically makes it a promising system towards adsorption of CO2 (∼90 mg/g) and methylene blue (∼248 mg/g). In addition, promising surface properties can be achieved after direct chemical activation of the raw hazelnut shells, preferably by H3PO4 (Specific Surface Area: 1918 m2/g, VP: 1.34 cm3/g, VMESO: 0.82 cm3/g, VMICRO: 0.50 cm3/g), but this choice is not the smartest, as it does not allow the valorization of the cellulose fraction to levulinic acid. Our approach paves the way for possible uses of these hydrochars originating from the levulinic acid chain for new environmental applications, thus smartly closing the biorefinery loop of the hazelnut shells

Biomass ethanolysis: process optimization and performances of ethyl levulinate as diesel blendstock

Biomass represents a key asset for renewable energy production in the context of the more and more pressing energetic transition. Moreover, at the present, the issue of how to store a convenient amount of energy on board of electric vehicles is still a challenge and electric vehicles perspectives are limited to passenger cars and very small-range trucks, significant amount of time being necessary to define the eventual appropriate electric storage system to be employed in heavy transport, as well in aviation and shipping. In this context alkyl levulinates represent a concrete perspective for partial replacement of fossil fuel with renewable blendstocks. In particular, ethyl levulinate (EL) production by direct acid-catalyzed biomass ethanolysis was studied in order to investigate and optimize this one-step process which involves only renewable starting materials (biomass and bioethanol). In this perspective, the role of the main reaction parameters as the substrate nature and loading, type of the acid catalyst and its concentration, reaction temperature and duration were studied. EL was tested up to high concentrations in a mixture with diesel fuel in a small single-cylinder air-cooled diesel engine, to verify the engine and emission performances of the different blend compositions respect to those ascertained with a conventional diesel fuel

A novel organosolv approach to allow efficient biomass fractionation and successive exploitation

The separation and exploitation of all three main components of lignocellulosic biomass represents a challenging target for biorefinery. In this perspective a novel strategy has been studied for the fractionation and integral exploitation of Arundo Donax L. biomass, a feedstock characterized by low cost, large availability, favourable composition and ability to grow in marginal lands unsuitable for agriculture, avoiding any competition with food chain. The adoption of n-butanol played a fundamental dual role: as fractionation organosolv agent to separate cellulose, hemicellulose, and lignin and also as reagent for the conversion of the obtained cellulose fraction to n-butyl levulinate. A preliminary hot water pre-treatment of the biomass for reducing the content of extractives makes the separation even more effective. A preliminary optimization of the main reaction conditions was performed