One step conversion of lignin from intact biomass to two phenol products, improving access to aromatics and fuels.

Biomass derived 5-hydroxymethylfurfural (HMF) has emerged as an important platform chemical for the production of value added chemicals and liquid fuels that are currently obtained from petroleum.Although a significant amount of research has been performed over the past decade, the high production cost of HMF is still a bottleneck for its sustainable utilization for making other value added chemicals and fuels on a commercial scale. Among several factors, low product selectivity and high purification cost are major constraints. To address these drawbacks, HMF production methodology in recent years has been directed towards utilization of biphasic media for concurrent extraction of HMF into an organic phase immediately after its formation in the reactive phase. As a result, several dozens of journal and patent articles have appeared, demonstrating the benefit of biphasic media for effective HMF extraction. This review article summarizes the findings of the most recent research articles with critical discussion on the factors that enhance the performance of biphasic media. Particular emphasis has been given to the development of more effective extracting solvents and their beneficial effect in enhancing HMF yield and selectivity, improvement of partition coefficient, mechanistic role of the bi-functional acid catalysts and factors that control high HMF selectivity for solid catalysts.

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The development of chemical methods for the direct catalytic conversion of biomass to high value organic molecules is an area of increasing interest. The plant matter component known as lignin is a polymer consisting of aromatic rings that could provide a means of obtaining aromatic materials currently derived solely from petroleum. This report describes a bimetallic Pd/C and Zn catalytic system that can perform selective hydrodeoxygenation (HDO) of monomeric lignin surrogates as well as successfully cleave the b-O-4 linkages found in dimeric lignin model complexes and synthetic lignin polymers with near quantitative conversions and yields between 80-90%. The reaction with lignin polymer was highly selective affording methoxy substituted propylphenol as the major product. These reactions were performed in a Parr reactor operating at relatively mild temperature (150 C) and pressure (20 bar H 2 ) using methanol as a solvent. Reaction products were characterized using high-pressure liquid chromatography coupled to a linear quadrupole ion trap mass spectrometer equipped with an electrospray ionization source using negative ion mode. Hydroxide ions were doped into the analyte solutions to encourage negative ion formation. This method ionizes all the mixture components to yield a single ion/analyte with no fragmentation. The catalyst is fully recyclable without the need for additional zinc. X-ray absorption spectroscopy (EXAFS) is consistent with Pd nanoparticles (4-5 nm) and no evidence of Pd-Zn alloy formation. A mechanistic hypothesis on the synergy between Pd and Zn is presented.

AlCl 3 •6H 2 O in a biphasic medium of water/tetrahydrofuran (THF) is effective for the synthesis of 5-hydroxymethylfurfural (HMF) from glucose-based carbohydrates. For glucose, an HMF yield of 61% was achieved in 10 min at 160 • C under microwave heating. The reaction time profile revealed the intermediacy of fructose en route to HMF with a dehydration rate constant that is approximately 4 times that of glucose isomerization to fructose. Addition of NaCl did not increase HMF yields significantly but it diminished lactic acid formation. Disaccharides (maltose and cellobiose) and starch gave good yields of HMF. However, cellulose required a higher temperature (180 • C) and longer reaction time (30 min) to give a modest yield of 37%. Several lignocellulosic biomass variants (corn stover, pine wood, grass, and poplar) were investigated with the AlCl 3 •6H 2 O biphasic system. The yields of HMF were modest (20-35%) but high concurrent yields of furfural were observed (51-66%). The described AlCl 3 •6H 2 O-NaCl-H 2 O/THF biphasic medium has potential because it is economic, nontoxic, and it exhibits fast kinetics (10 min) under microwave heating.

Lignin as a polymer of monomeric aromatic compounds retains great potential to be a source for liquid fuels and valuable chemicals. However, lignin from biomass has been traditionally treated as a waste byproduct and in most applications burned for its heat value. In this work, we report the catalytic conversion of lignin in Miscanthus into aromatic products by using earth-abundant Ni catalyst supported on activated carbon, under relatively mild conditions. The special ferulate linkage in grasses gives methyl ferulate ester and its derivatives, which were not observed for wood biomass substrates. By modification of the reaction conditions, saturated or unsaturated branched products can be obtained selectively. Optimal conditions give over 68% yield of select aromatic products from lignin. Furthermore, after lignin depolymerization and upgrading, the carbohydrates of miscanthus were recovered as a solid residue, which upon treatment with iron chloride produced useful platform chemicals (furfurals and levulinic acid). On the basis of our study, all three major components of biomass (lignin, cellulose and hemicellulose) are effectively utilized, with an overall 55% conversion of total accessible biomass into high value chemicals with 98% mass balance.

The peroxides from methylrhenium trioxide (MTO) and hydrogen peroxide, CH3ReO2(η2-O2), A, and CH3Re(O)(η2-O2)2(H2O), B, have been fully characterized in both organic and aqueous media by spectroscopic means (NMR and UV−vis). In aqueous solution, the equilibrium constants for their formation are K 1 = 16.1 ± 0.2 L mol-1 and K 2 = 132 ± 2 L mol-1 at pH 0, μ = 2.0 M, and 25 °C. In the presence of hydrogen peroxide the catalyst decomposes to methanol and perrhenate ions with a rate that is dependent on [H2O2] and [H3O+]. The complex peroxide and pH dependences could be explained by one of two possible pathways:  attack of either hydroxide on A or HO2 - on MTO. The respective second-order rate constants for these reactions which were deduced from comprehensive kinetic treatments are k A = (6.2 ± 0.3) × 109 and k MTO = (4.1 ± 0.2) × 108 L mol-1 s-1 at μ = 0.01 M and 25 °C. The plot of log k ψ versus pH for the decomposition reaction is linear with a unit slope in the pH range 1.77−6.50. The diperoxide B decomposes much more slowly to yield O2 and CH3ReO3. This is a minor pathway, however, amounting to <1% of the methanol and perrhenate ions produced from the irreversible deactivation at any given pH. Within the limited precision for this rate constant, it appears to vary linearly with [OH-] with k = 3 × 10-4 s-1 at pH 3.21, μ = 0.10 M, and 25 °C. Without peroxide, CH3ReO3 is stable below pH 7, but decomposes in alkaline aqueous solution to yield CH4 and ReO4 -. As a consequence, the decomposition rate rises sharply with [H2O2], peaking at the concentration at which [A] is a maximum, and then falling to a much smaller value. Variable-temperature 1H NMR experiments revealed the presence of a labile coordinated water in B, but supported the anhydride form for A.

Biomass is a promising feedstock for the next generation drop-in liquid fuels and renewable chemicals, and hence the development of economically viable technologies for the production of commodity and specialty chemicals from sustainable biomass have received significant attention in recent years.While biomass transformation into drop-in biofuels involves multiple processing steps in which biomass is first depolymerized and converted to furfurals (5hydroxymethylfurfural, furfural), catalytic upgrading of furfurals is the most important step in achieving end products of the desired fuel properties. Several research articles have been published in the past decade reporting homogeneous and heterogeneous catalytic processes for upgrading furfurals to relevant drop-in fuel candidates such as, 2,5-dimethylfuran (DMF), 2methylfuran (2-MF), 5-ethoxymethylfurfural (EMF), γ-valorolactone (GVL), ethyl levulinate and long chain hydrocarbon alkanes. Although process technologies for the production and upgrading of some of these fuel compounds have been reviewed, a concise overview on production methodologies for all relevant furan based fuel compounds, including long chain hydrocarbon alkanes, from furfurals is yet to be published. This review article is aimed atpresenting an up to date analysis of the reported catalytic technologies for upgrading furfurals into long chain hydrocarbons with special emphasis on the condensation reactions for producing high carbon chain precursors and catalytic systems for their subsequent deoxygenation to achieve high yield and selectivity in fuel grade hydrocarbons. The current state-of-the-art on upgrading furfurals to DMF, 2-MF and EMF are also analyzed.