László T. Mika

γ-Valerolactone—a sustainable liquid for energy and carbon-based chemicals

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.

Microwave-assisted conversion of carbohydrates to levulinic acid: an essential step in biomass conversion

Degradation of non-edible carbohydrates to levulinic acid (4-oxopentanoic acid) was studied by using dielectric heating with microwave energy. Levulinic acid and its reduced and dehydrated derivative, γ-valerolactone (GVL), can be used for the production of small-molecule, functionalized hydrocarbons, which might be potential platform molecules for the chemical industry. First, simple model compounds (fructose, glucose, saccharose and cellobiose) were hydrolyzed in order to find the optimum reaction conditions (e.g. reagent, reaction temperature, acid concentration, time) for the degradation and transformation of polysaccharides (cellulose, chitin, chitosan) by using controlled microwave irradiation. Cellulose, a non-edible biopolymer of plant origin, was successfully converted to levulinic acid under the optimized conditions (2 M H2SO4, 170 °C, 50 min) with a yield of 34.2% in a mono-mode Multisynth microwave reactor. The reactions proceeded with hydrochloric acid catalysis as well, and a slightly better yield was achieved, however, using HCl (a chlorine containing catalyst) raises serious environmental concerns. The hydrolysis of glucosamine-based glycans (D-glucosamine, N-Ac-D-glucosamine, LMw-chitosan, MMw-chitosan, chitin) was also studied and optimized with sulfuric acid as a catalyst in a mono-mode Multisynth microwave reactor. The highest yield of levulinic acid was obtained with 2 M H2SO4 at 190 °C for 30 min. N-Ac-D-glucosamine, D-glucosamine, LMw-chitosan and MMw-chitosan resulted in levulinic acid with yields between 20.6% and 32.7%, the larger molecular weight chitin was degraded to levulinic acid with a yield of 37.8%.

Catalytic Conversion of Carbohydrates to Initial Platform Chemicals: Chemistry and Sustainability

The replacement of fossil resources that currently provide more than 90% of our energy needs and feedstocks of the chemical industry in combination with reduced emission of carbon dioxide is one of the most pressing challenges of mankind. Biomass as a globally available resource has been proposed as an alternative feedstock for production of basic building blocks, which could partially or even fully replace the currently utilized fossil-based ones in well-established chemical processes. The destruction of lignocellulosic feed followed by oxygen removal from its cellulose and hemicellulose content by catalytic processes results in the formation of initial platform chemicals (IPCs). However, their sustainable production strongly depends on the availability of resources, their efficient or even industrially viable conversion processes, and replenishment time of feedstocks. Herein, we overview recent advances and developments in catalytic transformations of the carbohydrate content of lignocellulosic biomass to IPCs (i.e., ethanol, 3-hydroxypropionic acid, isoprene, succinic and levulinic acids, furfural, and 5-hydroxymethylfurfural). The mechanistic aspects, development of new catalysts, different efficiency indicators (yield and selectivity), and conversion conditions of their production are presented and compared. The potential biochemical production routes utilizing recently engineered microorganisms are reviewed, as well. The sustainability metrics that could be applied to the chemical industry (individual set of sustainability indicators, composite indices methods, material and energy flow analysis-based metrics, and ethanol equivalents) are also overviewed as well as an outlook is provided to highlight challenges and opportunities associated with this huge research area.

An improved catalytic system for the reduction of levulinic acid to γ-valerolactone

An improved bidentate phosphine-modified recyclable catalytic system was developed for the selective conversion of biomass-derived levulinic acid into γ-valerolactone with a TOF of 21 233 h−1 in solvent-, chlorine- and additive-free reaction environments.

Synthesis of γ-valerolactone using a continuous-flow reactor

This study describes the heterogeneous catalysed continuous synthesis of γ-valerolactone (GVL) using a continuous-flow reactor, H-Cube® and H-Cube Pro™, equipped with 5% Ru/C, 10% Pd/C and RANEY® Ni CatCart®. The highest yield of GVL was achieved by using 5% Ru/C in the presence of 0.015 mol L−1 Bu-P(C6H4-m-SO3Na)2 ligand under 100 bar H2 at 100 °C.

Direct asymmetric reduction of levulinic acid to gamma-valerolactone: synthesis of a chiral platform molecule

Levulinic acid was directly converted to optically active (S)-gamma-valerolactone, a proposed biomass-based chiral platform molecule. By using a SEGPHOS ligand-modified ruthenium catalyst in methanol as a co-solvent, eventually, 100% chemoselectivity, and 82% enantioselectivity were achieved. The effect of the catalyst composition and reaction parameters on the activity and selectivity was investigated in detail. The conversion of a “real” biomass derived levulinic acid to optically active GVL without decreasing the enantioselectivity was also demonstrated.

A step towards hydroformylation under sustainable conditions: platinum-catalysed enantioselective hydroformylation of styrene in gamma-valerolactone

Platinum-catalysed enantioselective hydroformylation of styrene was performed in γ-valerolactone (GVL) as a proposed environmentally benign reaction medium. Optically active bidentate ligands, possessing various types of chirality elements e.g. central (BDPP), axial (BINAP, SEGPHOS, DM-SEGPHOS, DTBM-SEGPHOS) and planar/central (JOSIPHOS) elements, were applied in in situ generated Pt-diphosphine-tin(II)chloride catalyst systems. In general, slightly higher activities and regioselectivities towards a branched aldehyde (2-phenylpropanal) were obtained in toluene as a reference conventional solvent. However, higher chemoselectivities towards aldehydes (up to 98%) in GVL were obtained at lower temperatures. The application of GVL proved to be also advantageous regarding enantioselectivity: although moderate enantioselectivities were obtained in both solvents, in most cases higher ee values were detected in GVL. From the mechanistic point of view, the formation of different catalytic intermediates and/or different kinetics can be envisaged from the different temperature dependences of ee in GVL and toluene. The 31P-NMR characterization of catalyst species in GVL was also provided.

Rhodium-catalyzed hydrogenation of olefins in γ-valerolactone-based ionic liquids

γ-Valerolactone-based ionic liquids were successfully used as the catalyst phase for [Rh(cod)2][BF4]/RP(C6H4-m-SO3Na)2 (R = Me, Pr, Bu, Cp) catalyzed hydrogenation of different olefins. Compared to broadly used ionic liquids e.g. 1-butyl-3-methylimidazolium chloride [bmim][Cl], the turnover frequencies were significantly higher and the reaction was selective for the CC double bonds in the presence of carbonyl, cyano, and phenyl groups. The catalyst was recycled for ten consecutive runs under regular or biphasic conditions without loss of activity. The vapour pressure and viscosity of γ-valerolactone-based ionic liquids were determined as well.

Production of platform molecules from sweet sorghum

This study proves that the non-food dedicated sweet sorghum (Sorghum bicolor) can be a possible source and/or raw material of platform molecules such as levulinic acid (LA) and 5-hydroxymethyl-2-furaldehyde (5-HMF). The high sugar-containing juice derived from sweet sorghum can be efficiently converted to LA and 5-HMF by using microwave dielectric heating. Centrifugal separation was proposed as a first step of the technology to remove the insoluble materials (fibers, starch, and sand) to obtain high sugar containing feedstock for acid-catalyzed dehydration. The effects of pretreatment by centrifugal separation and reaction conditions (irradiation time, acid concentration and reaction temperature) on the formation of levulinic acid were studied. The conversions were monitored by in situ NMR spectroscopy. It was shown that maximum yield (31.4%) of LA was achieved in the presence of 2 M sulfuric acid by applying 30 min irradiation at 160 °C to the sorghum sample treated for 20 min in a centrifuge at a rotational force of 5870. It was also revealed that 5-HMF can be produced from the sweet sorghum juice in the presence of 0.05 M sulfuric acid at 120 °C.

Catalytic transfer hydrogenation in γ-valerolactone-based ionic liquids

The combination of transfer hydrogenation reaction with the advantages of γ-valerolactone-based ionic liquids could result in an environmentally benign method for the reduction of organic substrates. Ionic liquids containing 4-hydroxyvalerate anion were applied as alternative solvents for the reduction of acetophenone, its substituted forms and different alkenes using transition metal based catalysts. The optimal conditions (e.g. type of catalyst precursor and hydrogen donor) for the transformation were also specified.