Boosting Dimethyl Carbonate Production from CO2 and Methanol using Ceria-Ionic Liquid Catalyst.

As a crucial strategy towards a sustainable chemical industry, the direct synthesis of dimethyl carbonate (DMC) from renewable carbon dioxide (CO2) and methanol (MeOH) is studied using CeO2 nanoparticles modified with 1-butyl-3-methylimidazolium hydrogen carbonate ([BMIm][HCO3]) devoid of stoichiometric dehydrating agents. The synthesized CeO2@[BMIm][HCO3] catalyst having high thermal stability harnesses the unique physicochemical properties of CeO2 and the ionic liquid to exhibit a DMC yield of 10.4 % and a methanol conversion of 16.1 % at optimal conditions (pressure of CO2=5 MPa; temperature=130 °C). The catalytic behavior of CeO2@[BMIm][HCO3] studied with a detailed XRD, XPS, CO2 and NH3-TPD, Raman spectroscopy, TGA, FTIR, SEM and TEM suggests that the synergy between the two catalytic components originating from an increased surface oxygen vacancies boosts the overall catalytic performance. After several recycling tests, the catalyst demonstrated no significant reduction in DMC yield and methanol conversion. This platform is an attractive approach to synthesize thermally stable nanoparticle@ionic liquid that retains and merges the physical attributes of both materials for producing useful bulk chemicals from readily available chemical resources.

Investigation of the thermal deconstruction of ß-ß' and 4-O-5 linkages in lignin model oligomers by density functional theory (DFT).

Model compounds that represent important substructures in lignin have popularly been used to gain a better understanding of the behavior of lignin during thermal deconstruction, such as fast pyrolysis. The ß-O-4 linkage of lignin has previously been the focus of many model compound studies as it is the most prevalent linkage found in native lignin. In this work, two lesser studied linkages, the ß-ß' and 4-O-5, were investigated with density functional theory (DFT). Bond dissociation enthalpies (BDEs) were calculated for the relevant bonds along each interunit linkage for two model compounds containing these linkages. Conformational analysis of the first model oligomer has a relative enthalpy difference of 1.55 kcal mol-1. For the ß-ß' linkage, the alpha carbons had the lowest BDEs of the ring opening reactions due to excessive electron delocalization around the aromatic rings. The bonds of the 4-O-5 linkage had similar BDEs but were appreciably higher than the BDEs for other ether linkages, such as ß-O-4 and α-O-4. The higher BDEs of the 4-O-5 bonds is a result of the radical being formed on an aromatic carbon compared to an aliphatic carbon. Our results indicate the ring-opening reactions around the alpha-carbon of the ß-ß' linkage would be a major reaction point during thermal deconstruction of the chosen oligomers. This work provides valuable information on the thermal deconstruction behavior of two lesser studied interunit linkages that builds on the authors' previous work, on ß-O-4, α-O-4, and ß-5 linkages, to develop a library of reaction information for various lignin interunit linkages.

Co-application of biochar and nitrogen fertilizer reduced nitrogen losses from soil.

Combined application of biochar and nitrogen (N) fertilizer has the potential to reduce N losses from soil. However, the effectiveness of biochar amendment on N management can vary with biochar types with different physical and chemical properties. This study aimed to assess the effect of two types of hardwood biochar with different ash contents and cation exchange capacity (CEC) on soil N mineralization and nitrous oxide (N2O) production when applied alone and in combination with N fertilizer. Soil samples collected from a temperate pasture system were amended with two types of biochar (B1 and B2), urea, and urea plus biochar, and incubated for 60 days along with soil control (without biochar or urea addition). Soil nitrate N, ammonium N, ammonia-oxidizing bacteria amoA gene transcripts, and N2O production were measured during the experiment. Compared to control, addition of B1 (higher CEC and lower ash content) alone decreased nitrate N concentration by 21% to 45% during the incubation period while the addition of B2 (lower CEC and higher ash content) alone increased the nitrate N concentration during the first 10 days. Biochar B1 also reduced the abundance of amoA transcripts by 71% after 60 days. Compared to B1 + urea, B2 + urea resulted in a significantly greater initial increase in soil ammonium and nitrate N concentrations. However, B2 + urea had a significantly lower 60-day cumulative N2O emission compared to B1 + urea. Overall, when applied with urea, the biochar with higher CEC reduced ammonification and nitrification rates, while biochar with higher ash content reduced N N2O production. Our study demonstrated that biochar has the potential to enhance N retention in soil and reduce N2O emission when it is applied with urea, but the specific effects of the added biochar depend on its physical and chemical properties.

Structural changes in lignocellulosic biomass during activation with ionic liquids comprising 3-methylimidazolium cations and carboxylate anions.

BACKGROUND: Lignocellulosic biomass requires either pretreatment and/or fractionation to recover its individual components for further use as intermediate building blocks for producing fuels, chemicals, and products. Numerous ionic liquids (ILs) have been investigated for biomass pretreatment or fractionation due to their ability to activate lignocellulosic biomass, thereby reducing biomass recalcitrance with minimal impact on its structural components. In this work, we studied and compared 1-allyl-3-methylimidazolium formate ([AMIM][HCOO]) to the commonly used 1-ethyl-3-methylimidazolium acetate ([EMIM][CH3COO]) for its potential to activate hybrid poplar biomass and enable high cellulose and hemicellulose enzymatic conversion. Although [EMIM][CH3COO] has been widely used for activation, [AMIM][HCOO] was recently identified to achieve higher biomass solubility, with an increase of 40% over [EMIM][CH3COO]. RESULTS: Since IL activation is essentially an early stage of IL dissolution, we assessed the recalcitrance of [EMIM][CH3COO] and [AMIM][HCOO]-activated biomass through a suite of analytical tools. More specifically, Fourier transform infrared spectroscopy and X-ray diffraction showed that activation using [AMIM][HCOO] does not deacetylate hybrid poplar as readily as [EMIM][CH3COO] and preserves the crystallinity of the cellulose fraction, respectively. This was supported by scanning electron microscopy and enzymatic saccharification experiments in which [EMIM][CH3COO]-activated biomass yielded almost twice the cellulose and hemicellulose conversion as compared to [AMIM][HCOO]-activated biomass. CONCLUSION: We conclude that the IL [AMIM][HCOO] is better suited for biomass dissolution and direct product formation, whereas [EMIM][CH3COO] remains the better IL for biomass activation and fractionation.

Relationship between lignocellulosic biomass dissolution and physicochemical properties of ionic liquids composed of 3-methylimidazolium cations and carboxylate anions.

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIM]Acetate) has been widely used for biomass processing, i.e., to pretreat, activate, or fractionate lignocellulosic biomass to produce soluble sugars and lignin. However, this IL does not achieve high biomass solubility, therefore minimizing the efficiency of biomass processing. In this study, [EMIM]Acetate and three other ILs composed of different 3-methylimidazolium cations and carboxylate anions ([EMIM]Formate, 1-allyl-3-methylimidazolium ([AMIM]) formate, and [AMIM]Acetate) were analyzed to relate their physicochemical properties to their biomass solubility performance. While all four ILs are able to dissolve hybrid poplar under fairly mild process conditions (80 °C and 100 RPM stirring), [AMIM]Formate and [AMIM]Acetate have particularly increased biomass solubility of 40 and 32%, respectively, relative to [EMIM]Acetate. Molecular dynamics simulations suggest that strong interactions between IL and specific plant biopolymers may contribute to this enhanced solubilization, as the calculated second virial coefficients between ILs and hemicellullose are most favorable for [AMIM]Formate, matching the trend of the experimental solubility measurements. The simulations also reveal that the interactions between the ILs and hemicellulose are an important factor in determining the overall biomass solubility, whereas lignin-IL interactions were not found to vary significantly, consistent with literature. The combined experimental and simulation studies identify [AMIM]Formate as an efficient biomass solvent and explain its efficacy, suggesting a new approach to rationally select ionic liquid solvents for lignocellulosic deconstruction.

Kinetics of the release of elemental precursors of syngas and syngas contaminants during devolatilization of switchgrass.

In this study, the results from laboratory measurements of the devolatilization kinetics of switchgrass in a rapidly heated fixed bed reactor flushed with argon and operated at constant temperatures between 600 and 800°C was reported. Results indicate that switchgrass decomposes in two sequential stages during pyrolysis: stage I involves the evaporation and devolatilization of water and extractives and stage II involves that of hemicellulose, cellulose, and lignin. The estimated global activation energy for stage II increased from 52.80 to 59.39kJ/mol as the reactor temperature was increased from 600 to 800°C. The maximum conversion of carbon, hydrogen, oxygen, sulfur, and nitrogen ranged from 0.68 to 0.70, 0.90 to 0.95, 0.88 to 0.91, 0.70 to 0.80, and 0.55 to 0.66, respectively. The retention of alkali and alkaline earth metal (AAEM) species in the solid char after complete pyrolysis was significantly higher than in the original feed, indicating the importance of AAEM species in subsequent char processing.