Conversion of biomass into value-added chemicals

The greenhouse gas (GHG) emissions reduction potentials of various near- and long-term transportation technologies were estimated. The estimated per-travel-distance GHG emissions results indicate that alternative transportation fuels and advanced vehicle technologies can help to significantly reduce transportation-related GHG emissions. Of the near-term technologies evaluated, electric vehicles, hybrid electric vehicles, compression-ignition, direct-injection vehicles, and E85 (85 percent ethanol and 15 percent gasoline) flexible-fuel vehicles can reduce fuelcycle GHG emissions by more than 25 percent on a fuel-cycle basis. Electric vehicles powered by electricity generated primarily from nuclear and renewable sources can reduce GHG emissions by 80 percent. Other alternative fuels (such as compressed natural gas and liquefied petroleum gas) offer limited, but positive, GHG emissions reduction benefits. Among the long-term technologies evaluated, conventional sparkignition and compression-ignition engines powered by alternative fuels and gasoline- and diesel-powered advanced vehicles can reduce GHG emissions by 10 to 30 percent. Dedicated ethanol vehicles, electric vehicles, hybrid electric vehicles, and fuel-cell vehicles can reduce GHG emissions by more than 40 percent. Spark-ignition engines and fuel-cell vehicles powered by cellulosic ethanol and solar hydrogen (for fuel-cell vehicles only) can reduce GHG emissions by over 80 percent. In conclusion, both near- and long-term alternative fuels and advanced transportation technologies can play a role in reducing GHG emissions from the transportation sector.

In this work, molecular dynamics (MD) simulations were carried out to study the behaviors of a binary ionic liquid (IL) mixture consisting of equimolar [C2C1Im][BF4] and [C4C1Im][BF4], as well as two corresponding pure ILs, at the liquid-vacuum interface. Our simulation results show that the competition of nonpolar interactions between different alkyl chains of two cations results in an obvious surface segregation behavior of the IL mixture at the interface, indicating an enhanced aggregation of the [C4C1Im]+ cations but a weakened aggregation of the [C2C1Im]+ cations at the outermost surface. More interestingly, different hydrogen bond (HB) changes between two imidazolium cations at the interface can be driven by such surface segregation behavior, where the [C2C1Im]+ cations rather than the [C4C1Im]+ ones have more and stronger HBs with the [BF4]- anions by comparison with the corresponding pure ILs at the interface. Meanwhile, it is interesting to find that such a stronger HB would lower the rotations of the imidazolium rings of interfacial [C2C1Im]+ cations. By contrast, the [C4C1Im]+ cations at the outermost surface rotate faster owing to their weaker HB. In addition, the orientation analysis uncovers that there is a major decrease for the orderliness of interfacial [C2C1Im]+ cations, but a minor decrease for that of interfacial [C4C1Im]+ cations, from the pure IL to the IL mixture. Such distinct results are closely related to the surface segregation between the [C2C1Im]+ and [C4C1Im]+ cations in the IL mixture and their interfacial HB properties. Thus, our simulation results afford a deep insight into the surface segregation effect on the HB behavior of the imidazolium-based IL mixture at liquid-vacuum interface.

The synthesis of nanoparticles by combinatorial sputtering in ionic liquids is a versatile approach for discovering new materials. Whereas the influence on nanoparticle formation of different pure ionic liquids has been addressed, the influence of (I) dilution of ionic liquid with solvents and (II) different mixtures of ionic liquids is less known. Therefore, mixtures of the ionic liquid [Bmim][(Tf)2N] with the organic solvent anisole and other ionic liquids ([Bmim][(Pf)2N], [BmPyr][(Tf)2N]) were used as liquid substrates for the sputter synthesis of nanoparticles, in order to investigate the influence of these mixtures on the size of the nanoparticles. First, mixtures of anisole with a suspension of sputtered Ag nanoparticles in [Bmim][(Tf)2N] were prepared in different volumetric steps to investigate if the stabilization of the NPs by the ionic liquid could be reduced by the solvent. However, a continuous reduction in nanoparticle size and amount with increasing anisole volume was observed. Second, Ag, Au and Cu were sputtered on ionic liquid mixtures. Ag nanoparticles in [Bmim][(Tf)2N]/[Bmim][(Pf)2N] mixtures showed a decrease in size with the increasing volumetric fraction of [Bmim][(Tf)2N], whereas all nanoparticles obtained from [Bmim][(Tf)2N]/[BmPyr][(Tf)2N] mixtures showed increasing size and broadening of the size distribution. Maximum sizes of sputtered Ag and Au NPs were reached in mixtures of [Bmim][(Tf)2N] with 20 vol.% and 40 vol.% [BmPyr][(Tf)2N]. The results indicate that ionic liquid mixtures with different portions of cations and anions have the capability of influencing the ionic liquid stabilization characteristics with respect to, e.g., nanoparticle size and size distribution.

Life-cycle assessment of alternative liquid fuels production in China

Perturbed-chain statistical associating fluid theory (PC-SAFT) was applied for modeling the vapor–liquid equilibrium of CO2 + toluene + ionic liquid (IL) mixtures and the molar volume of their liquid phases at temperatures between 298.15 K and 333.15 K and at pressures up to 80 bar. ILs used for this study contain the bis(trifluoromethylsulfonylimide) anion ([Tf2N]−) and imidazolium, pyridinium, thiolanium, and phosphonium cations. The pure-IL PC-SAFT parameters were fit to pure-IL liquid density data. Temperature-dependent binary interaction parameters were fit to binary liquid–liquid equilibrium data (i.e., toluene + IL) obtained from the literature and some points measured for this work. Temperature independent binary interaction parameters were fit to vapor–liquid equilibrium data (CO2 + IL, CO2 + toluene) from the literature. The availability of the pure-IL parameters and binary interaction parameters allowed prediction of CO2 solubility in toluene + IL mixtures with an absolute average relative deviation (AARD) of 6.8%, as well as molar volumes of CO2 + toluene + IL mixtures with an AARD of 5.0%, for the four ternary systems under investigation.

Lignin is one of the most abundant renewable raw materials available on earth and it has the potential to yield valuable low molecular weight aromatic compounds if it can be depolymerized selectively. Despite its unique characteristics as a natural product with multiple chemical and biophysical functionalities, it is largely under-exploited, because of the lack of available methods that effect depolymerization in a selective manner. One of the dominant linkages in lignin has a similar aryl ether structure to poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). There is evidence that the formation of PPO by an oxidative coupling polymerization of 2,6-dimethyl phenol (DMP) involves a redistribution mechanism. The most likely pathway involves the formation of a quinone ketal intermediate. This ketal unit can be either be redistributed (dissociated) or undergo an intramolecular rearrangement. Considering the reversibility of the redistribution mechanism in PPO polymerization and the existence of the same structural moiety in lignin, selective depolymerization of lignin may be effectively carried out under conditions favouring the redistribution mechanism. The focus of this thesis is to exploit PPO as a model polymer for lignin depolymerization and repolymerization in water and ionic liquids. The same methodology will be applied to lignin using a range of reaction conditions in an attempt to effect depolymerization to provide useful oligomers and monomers, which can be subsequently repolymerized to produce biomass derived plastics. In this research PPO was synthesized using different chemical and enzymatic catalysts and depolymerization of the PPO was achieved in water and ionic liquid with 4-tert-butyl-2,6-dimethylphenol (TBDMP) and 2,6-dimethylphenol (DMP) under oxidative conditions. Applying the same olptimized conditions used for PPO, lignin depolymerization was achieved, involving the redistribution mechanism under controlled mild conditions. Furthermore, several lignin-based copolymers (polyester-based and polyurethane-based) were then synthesised using depolymerized oligomeric lignins. The molecular weight of the all depolymerized products and lignin based copolymers was determined by gel permeation chromatography (GPC). The depolymerized products and newly formed lignin based copolymers were further analyzed by nuclear magnetic resonance (NMR) and infrared (IR). Thermal properties of lignin based copolymers were also evaluated using thermoanalytical techniques including thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Overall these studies demonstrated that PPO can be successfully depolymerized in water and ionic liquid. The potential for controlling the extent of depolymerization and the molecular weight of the depolymerized oligomers by using solvents where the solubility of PPO is limited was demonstrated. Moreover, it has been demonstrated that lignins can be extensively depolymerized under oxidative conditions using Cu(II) complexes and a monomeric para-blocked phenol (TBDMP). Novel lignin based thermoplastic copolyester was successfully synthesised by the esterification of oligomeric lignin with sebacoyl chloride in the presence of Triethylamine (TEA) as a base. Furthermore, several attempts were made to successfully synthesise lignin based polyurethane via a reaction of depolymerized lignin with aliphatic diisocyanate.

Ionic liquids are promising candidates for electrolytes in energy-storage systems. We demonstrate that mixing two ionic liquids allows to precisely tune their physical properties, like the dc conductivity. Moreover, these mixtures enable the gradual modification of the fragility parameter, which is believed to be a measure of the complexity of the energy landscape in supercooled liquids. The physical origin of this index is still under debate; therefore, mixing ionic liquids can provide further insights. From the chemical point of view, tuning ionic liquids via mixing is an easy and thus an economic way. For this study, we performed detailed investigations by broadband dielectric spectroscopy and differential scanning calorimetry on two mixing series of ionic liquids. One series combines an imidazole based with a pyridine based ionic liquid and the other two different anions in an imidazole based ionic liquid. The analysis of the glass-transition temperatures and the thorough evaluations of the measured dielectric permittivity and conductivity spectra reveal that the dynamics in mixtures of ionic liquids are well defined by the fractions of their parent compounds.

Use of solvents and environmental friendly materials for applications in Green Chemistry

In this work, the two mixtures of ionic liquid 1-n-propyl-4-amino-1,2,4-triazolium bromide and each type of the aggregated single-walled carbon nanotubes (SWCNTs), i.e. bundled SWCNTs and non-bundled, were investigated using molecular dynamics (MD) simulations. The structural characteristics of a SWCNT in the ionic liquid (IL) were examined by analyzing the radial distribution functions and the results show that the nearest IL cations to the SWCNT surface can approach it from three different positions. Also, the possibility of the dispersion of the bundled SWCNTs containing three and seven carbon nanotubes was investigated. The obtained results showed that under the investigated conditions, the IL cannot disperse the bundled SWCNTs, but it can disperse six and seven aggregated non-bundled ones. Moreover, we investigated the underlying dispersion mechanism of the aggregated SWCNTs in the IL, using MD simulations. The self diffusion coefficients and transport numbers of the cations and anions were computed in the systems containing pure IL, the mixtures of IL and one, six and seven non-bundled SWCNTs and the systems containing IL and bundled SWCNTs with three and seven carbon nanotubes. The obtained results showed that the diffusion coefficients and the transport numbers of the cations are more than anions in all mentioned systems.

The mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) ionic liquids (ILs) and water as a function of IL concentrations have been investigated by Fourier transform infrared (FTIR) spectroscopy and ultrafast two-dimensional IR (2D IR) spectroscopy. FTIR spectra of the mixtures resolve two different types of water species, one interacting with the BF4- anions and the other associated with bulklike water molecules. These two water species are in a dynamic equilibrium through forming different hydrogen bonding configurations which are separated by more than 100 cm-1 in the IR spectra. The structural dynamics of the IL mixtures are further revealed by monitoring the vibrational relaxation dynamics of the OD stretching group of interfacial water molecules hydrogen bonded to BF4- anions. With the increase of the IL bulk concentration, vibrational population and rotational dynamics of the interfacial water molecules can be described by a biexponential decay function and are strongly dependent on the IL concentrations. Furthermore, the ultrafast hydrogen bond exchanging between water and BF4- anions in the ILs are also measured using 2D IR spectroscopy. The average hydrogen bond exchanging rate is determined to be 19 ± 4 ps, which is around 3 times slower than that in the NaBF4 electrolyte aqueous solution. The much slower hydrogen bond exchanging rate indicates that the local structure of ILs and water molecules are strongly mediated by the steric effect of the cationic group in the ILs, which is proposed to be responsible for the formation of the heterogeneous structure in the IL mixtures. By using SCN- as the anionic probe, the structural inhomogeneity in the IL solutions can be confirmed from the distinct rotational dynamics of the SCN-, which is segregated from the rotational dynamics of water molecules in the IL mixtures.

We examine the life cycles of gasoline, diesel, compressed natural gas (CNG), and ethanol (C2H5OH)-fueled internal combustion engine (ICE) automobiles. Port and direct injection and spark and compression ignition engines are examined. We investigate diesel fuel from both petroleum and biosources as well as C2H5OH from corn, herbaceous bio-mass, and woody biomass. The baseline vehicle is a gasoline-fueled 1998 Ford Taurus. We optimize the other fuel/powertrain combinations for each specific fuel as a part of making the vehicles comparable to the baseline in terms of range, emissions level, and vehicle lifetime. Life-cycle calculations are done using the economic input-output life-cycle analysis (EIO-LCA) software; fuel cycles and vehicle end-of-life stages are based on published model results. We find that recent advances in gasoline vehicles, the low petroleum price, and the extensive gasoline infrastructure make it difficult for any alternative fuel to become commercially viable. The most attractive alternative fuel is compressed natural gas because it is less expensive than gasoline, has lower regulated pollutant and toxics emissions, produces less greenhouse gas (GHG) emissions, and is available in North America in large quantities. However, the bulk and weight of gas storage cylinders required for the vehicle to attain a range comparable to that of gasoline vehicles necessitates a redesign of the engine and chassis. Additional natural gas transportation and distribution infrastructure is required for large-scale use of natural gas for transportation. Diesel engines are extremely attractive in terms of energy efficiency, but expert judgment is divided on whether these engines will be able to meet strict emissions standards, even with reformulated fuel. The attractiveness of direct injection engines depends on their being able to meet strict emissions standards without losing their greater efficiency. Biofuels offer lower GHG emissions, are sustainable, and reduce the demand for imported fuels. Fuels from food sources, such as biodiesel from soybeans and C2H5OH from corn, can be attractive only if the co-products are in high demand and if the fuel production does not diminish the food supply. C2H5OH from herbaceous or woody biomass could replace the gasoline burned in the light-duty fleet while supplying electricity as a co-product. While it costs more than gasoline, bioethanol would be attractive if the price of gasoline doubled, if significant reductions in GHG emissions were required, or if fuel economy regulations for gasoline vehicles were tightened.

While known for a higher power density than batteries, electrochemical capacitors are limited by their energy density for some energy storage applications. Since the energy density of the device is proportional to the square of operating potential window, an effective way to increase energy density of the device is by increasing the window. Ionic liquid electrolytes are beneficial for this reason since they can theoretically operate at up to 6 V, though experimentally, the value is between 3-4 V, depending on the properties of electrode materials. By employing a novel electrochemical technique to study symmetric supercapacitors with carbon electrodes and ionic liquid electrolytes, we have found one of the possible reasons for the observed smaller operating potential window of ionic liquids in practical applications. We observed that even for a symmetric device, the different properties of the cation and anion results in an asymmetric performance of the two electrodes. However, a solution to this asymmetry is found by mixing two ionic liquids with the same cation, which ultimately results in a higher operating potential window of the device and therefore a higher energy density.1 Onion-like carbon (OLC) was used as the electrode material due to its large (>500 m2/g) outer surface available for ion adsorption and double layer formation, and no internal porosity that could restrict the movement of ions.2 However, electrode materials can also be made from high surface area carbons that contain a network of pores (e.g., activated or carbide-derived carbon) in which ions are adsorbed during charging. Though they boast a large operating potential window, ionic liquids are known to contain large and bulky ions. This can make it difficult to use an ionic liquid on a porous carbon with a range of pore sizes, some being smaller than the ion size, even though the specific surface area of the electrode material measured by gas adsorption is high and therefore the energy storage capability is more impressive. It has also been shown that the capacitance of porous electrodes is maximized when the ion size and pore size are equal.3 In this case, the ion is small enough to fit inside the pores while still large enough to take advantage of the surface area within the pore walls. While materials with a large outer surface allow a more accessible surface for adsorbing large ions, their capacitance is limited by their specific surface area. By designing an electrolyte based on mixed ionic liquids, we can match the ions in the mixture to the multiple pore sizes of the electrode material. Recently, it was found that the capacitance of porous carbon could be increased with the presence of multiple ions in the electrolyte mixture. Imidazolium-based ionic liquids are chosen based on their variable alkyl chain length which alters the cation size and bis(trifluoromethylsulfonyl)- imide (TFSI) is chosen as the anion for all ionic liquids. Different porous carbons with varying pore size distributions are used to illustrate the effect of ionic liquid mixture electrolytes. Finally, it has been shown previously that ionic liquid mixture electrolytes can be used to increase the operating temperature window of a supercapacitor to -50 °C – 100 °C.4 Ionic liquid mixtures have therefore been shown to improve the potential window, the capacitive performance, and the temperature window of supercapacitors, becoming an important area of study in the field of energy storage. 1. Van Aken, K. L., Beidaghi, M. & Gogotsi, Y. Formulation of Ionic-Liquid Electrolyte to Expand the Voltage Window of Supercapacitors. Angew. Chemie 127, 4888–4891 (2015). 2. McDonough, J. K. et al. Influence of the structure of carbon onions on their electrochemical performance in supercapacitor electrodes. Carbon N. Y. 50, 3298–3309 (2012). 3. Lin, R. et al. Solvent effect on the ion adsorption from ionic liquid electrolyte into sub-nanometer carbon pores. Electrochim. Acta 54, 7025–7032 (2009). 4. Lin, R. et al. Capacitive Energy Storage from -50 to 100 C Using an Ionic Liquid Electrolyte. J. Phys. Chem. Lett. 2, 2396–2401 (2011). Figure 1

Steady-state and time-resolved infrared spectroscopy of the azide (N(3)-) anion has been used to characterize aqueous mixtures both with the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF(4)]) and with dimethyl sulfoxide (DMSO). In the DMSO-water mixtures, two anion vibrational bands are observed for low water mole fractions (0 > X(w) > 0.25), which indicates a heterogeneous ion solvation environment. The band at 2000 cm(-1) observed for neat DMSO does not shift but decreases in amplitude as the amount of water is increased. Another band appears at slightly higher frequency at low X(w) (=0.05). As the amount of water is increased, this band shifts to higher frequency and becomes stronger and is attributed to azide with an increasing degree of hydration. At intermediate and high X(w), a single band is observed that shifts almost linearly with water mole fraction toward the bulk water value. The heterogeneity is evident from the infrared pump-probe studies in which the decay times depend on probe frequency at low mole fraction. For the azide spectra in IL-water mixtures, a single azide band is observed for each mole fraction mixture. The azide band shifts almost linearly with mole fraction, indicating nearly ideal mixing behavior. As with the DMSO-water mixtures, the time-resolved IR decay times are probe-frequency-dependent at low mole fraction, again indicating heterogeneous solvation. In both the DMSO and IL mixtures with water, the relaxation times are slower than would be expected from ideal mixing, suggesting that vibrational relaxation of azide is more sensitive than its vibrational frequency to the solvent structure. The results are discussed in terms of preferential solvation and the degree to which the azide shift and vibrational relaxation depend on the degree of water association in the mixtures.

In a recent article ( J. Phys. Chem. C 2019, 123, 4914−4925) we studied using molecular dynamics simulations the structure of an ionic liquid (IL) mixture comprised of 1-methyl-3-octylimidazolium octylsulfate and 1-ethyl-3-methylimidazolium ethylsulfate confined by vacuum interfaces. At these interfaces, the mixture formed an apolar blocking layer concealing the smaller and more polar ions to the interior of the liquid phase. In the current work, and for the same IL mixture, we study the case of confinement between (001) mica surfaces, where the solid provides a flat and polar ionic interface. Our focus is twofold; first, we want to understand the structural and dynamical behaviors of the IL mixture at the boundary where the confining interface is highly polar, and second we want to establish how far away from the interface liquid behavior is recovered. This last point is particularly important in light of puzzling recent experimental results regarding the behavior of ILs and solutes dissolved in them under confinement, where large distances appear to be necessary to recover true bulk behavior. We find that the IL mixture is highly structured at the adlayer, but within 5 nm bulk-like structural features are recovered. Dynamical properties at the center of our thin film also appear converged to bulk behavior, but further studies are required to fully address the issue of dynamics within confined IL films.

Biochar, compost and biochar-compost: effects on crop performance, soil quality and greenhouse gas emissions in tropical agricultural soils