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المؤلفون: Wee Y. Lim, James A. Dumesic, Stephanie G. Wettstein, Elif I. Gürbüz, Jean Marcel R. Gallo, David Martin Alonso
المصدر: Angewandte Chemie. 125:1308-1312
مصطلحات موضوعية: chemistry.chemical_classification, Aqueous solution, Water, Lignocellulosic biomass, Mineral acid, General Chemistry, General Medicine, Xylose, Furfural, Catalysis, Furfuryl alcohol, Lactones, chemistry.chemical_compound, chemistry, Polysaccharides, Zeolites, Organic chemistry, Hemicellulose
الوصف: The effective conversion of lignocellulosic biomass into fuels and chemicals requires the utilization of both hemicellulose and cellulose, consisting primarily of C5 and C6 sugars, respectively. Catalytic conversion strategies for hemicellulose are of particular importance because biological conversion of C5 sugars is not as efficient as the conversion of C6 sugars. In addition, C5 sugars/oligomers are produced as a side stream in the pulp and paper industry, which provides an opportunity to create value-added products. Among the products that can be obtained from C5 sugars, furfural is a particularly promising option, as it can replace crude-oil-based organics for the production of resins, lubricants, adhesives, and plastics, as well as valuable chemicals, such as furfuryl alcohol and tetrahydrofurfuryl alcohol. Current methods for production of furfural from hemicellulose use mineral acid catalysts which are corrosive, difficult to recover from the reaction mixture, and pose environmental and health risks. Importantly, current yields for the production of furfural in water are low (e.g., < 60%). Biphasic systems improve the yield of furfural and its separation from the mineral acid, and can be employed for lignocellulosic biomass which has been pretreated with mineral acids. Ideally, it is desirable to replace mineral acids with solid acids in lignocellulose processing. However, the use of solid acid catalysts in an aqueous environment is challenging in view of catalyst degradation and/or leaching in aqueous solution at elevated temperatures (e.g., 430 K). Moreover, biphasic systems typically require the use of salts to achieve good separation of the phases and to improve the efficiency of the extracting organic layer, and solid catalysts cannot be used in this case because the exchange of protons on the catalyst with cations in solution leads to deactivation of the heterogeneous catalyst. The aforementioned difficulties associated with the conversion of xylose into furfural can be alleviated by using gvalerolactone (GVL) as a solvent in a monophasic system with solid acid catalysts. Importantly, GVL is a solvent which can be produced from lignocellulose, and Horvath and coworkers have been strong proponents for the use of GVL as a solvent in biomass processing. Using GVL as the solvent increases the rate of xylose conversion and decreases the rates of furfural degradation reactions. In addition, furfural has a higher volatility than GVL and can thus be obtained as a top product in a distillation step. Alternatively, GVL, a valuable chemical with multiple uses, can be synthesized as the end product of the process, thereby eliminating product purification steps. Furthermore, the use of a monophasic reaction system eliminates the loss of the product in the aqueous phase, the need for a liquid–liquid separation step, and reduces mixing requirements. Additionally, by minimizing the concentration of water present in the reactor, it is possible to use solid catalysts for the conversion of xylose (and xylose oligomers) into furfural with minimal degradation of the catalyst and without leaching of acid sites into solution. Figure 1 shows the furfural yields achieved, after complete xylose conversion, for different solid acid catalysts. The catalysts contained Bronsted and/or Lewis acid sites, and just GVL was used as the solvent. Even though water was not added in the reaction mixture, it is a by-product of dehydration, and its concentration can reach up to 0.7 wt% with quantitative yields of furfural. Catalysts, such as g-Al2O3 (galumina), Sn-SBA-15, and Sn-beta, which contain only Lewis acid sites, resulted in the lowest yields of furfural (see Figure S1 in the Supporting Information for FTIR measure
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المؤلفون: Dong Wang, David Martin Alonso, Jesse Q. Bond, James A. Dumesic
المصدر: Journal of Catalysis. 281:290-299
مصطلحات موضوعية: chemistry.chemical_classification, Valerolactone, Decarboxylation, Kinetics, Heterogeneous catalysis, Butene, Catalysis, chemistry.chemical_compound, chemistry, Organic chemistry, Physical and Theoretical Chemistry, Bond cleavage, Lactone
الوصف: Reaction kinetic studies were carried out of the reversible interconversion between γ- valerolactone (GVL) and pentenoic acid (PEA) combined with the irreversible decarboxylation of both species to form butene and CO 2 over a SiO 2 /Al 2 O 3 catalyst at pressures from atmospheric to 36 bar, temperatures from 498 to 648 K, different concentrations of GVL and PEA, as well as in the presence of water. The catalyst exhibited reversible deactivation within the initial 24 h on stream (losing about 50% of the initial catalytic activity), followed by a slower rate of deactivation of roughly 0.4–0.5% per hour on stream. Decarboxylation of γ -valerolactone, producing equimolar quantities of butene and CO 2 , may possibly occur by two distinct pathways: a direct route from the lactone and an indirect route from PEA. 1-butene is the primary product of decarboxylation, formed via β-scission of intermediate carbenium ions. The apparent activation barrier for decarboxylation of GVL (175 kJ mol −1 ) is higher than for decarboxylation of PEA (142 kJ mol −1 ). A simple kinetic model with rate expressions accounting for adsorption and unimolecular surface reactions of GVL and PEA is sufficient to describe the trends measured for the rates of GVL ring opening to PEA, GVL decarboxylation, PEA cyclization to GVL, and PEA decarboxylation at different reaction conditions.
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المؤلفون: Clare P. Grey, C. David Martin, John B. Parise, Nancy S. Goroff, Samrat Chawda, Joseph W. Lauher, Christopher Wilhelm, Jeffrey A. Webb, Gary P. Halada, Frank W. Fowler, Cathy Tarabrella, Stephen A Boyd, Liang Luo
المصدر: Journal of the American Chemical Society. 130:4415-4420
مصطلحات موضوعية: chemistry.chemical_classification, Diacetylene, macromolecular substances, General Chemistry, Polymer, Conjugated system, Biochemistry, Catalysis, chemistry.chemical_compound, symbols.namesake, PIDA, End-group, Colloid and Surface Chemistry, Monomer, chemistry, Polymerization, Polymer chemistry, symbols, Raman spectroscopy
الوصف: Diiodobutadiyne forms cocrystals with bis(pyridyl)oxalamides in which the diyne alignment is near the ideal parameters for topochemical polymerization to the ordered conjugated polymer, poly(diiododiacetylene) (PIDA). Nonetheless, previous efforts to induce polymerization in these samples via heat or irradiation were unsuccessful. We report here the successful ordered polymerization of diiodobutadiyne in these cocrystals, by subjecting them to high external pressure (0.3-10 GPa). At the lower end of the pressure range, the samples contain primarily monomer, as demonstrated by X-ray diffraction studies, but some polymerization does occur, leading to a pronounced color change from colorless to blue and to the development of intense Raman peaks at 962, 1394, and 2055 cm-1, corresponding to the poly(diacetylene). At higher pressures, the samples turn black and contain primarily polymer, as determined by solid-state NMR and Raman spectroscopy. Both density functional theory calculations (B3LYP/LanL2DZ) and comparisons to authentic samples of PIDA have confirmed the data analysis.
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المصدر: Energy & Environmental Science. 5:8199
مصطلحات موضوعية: chemistry.chemical_classification, Aqueous solution, Renewable Energy, Sustainability and the Environment, Chemistry, Salt (chemistry), Pollution, Catalysis, gamma-Valerolactone, Solvent, chemistry.chemical_compound, surgical procedures, operative, Nuclear Energy and Engineering, immune system diseases, Humin, Levulinic acid, Environmental Chemistry, Organic chemistry, Cellulose
الوصف: Cellulose deconstruction at 428 K was studied in biphasic reaction systems consisting of GVL and aqueous solutions containing HCl (0.1–1.25 M) and a solute, such as salt or sugar. This biphasic system achieves high yields of levulinic and formic acids (e.g., 70%), and leads to complete solubilization of cellulose. The GVL solvent extracts the majority of the levulinic acid (e.g., greater than 75%), which can subsequently be converted to GVL over a carbon-supported Ru–Sn catalyst. This approach for cellulose conversion eliminates the need to separate the final product from the solvent, because the GVL product is the solvent. In addition, this approach eliminates the deposition of solid humin species in the cellulose deconstruction reactor, allowing these species to be collected and used for other processing options.
URL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_________::d8bd123813c6714db492132bf9439b7c
https://doi.org/10.1039/c2ee22111j -
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المصدر: Green Chemistry. 12:992
مصطلحات موضوعية: chemistry.chemical_classification, Aqueous solution, Alkene, Nonene, Alcohol, Pollution, Heptene, Catalysis, chemistry.chemical_compound, Hydrocarbon, chemistry, Hexene, Environmental Chemistry, Organic chemistry
الوصف: A process is described to produce renewable liquid fuels, similar to existing petroleum-derived transportation fuels, through the oligomerization over solid acid catalysts of C9-alkenes derived from γ-valerolactone (GVL). Larger, non-terminal alkenes are shown to be less reactive than short chain α-alkenes for oligomerization over solid acid sites, and Amberlyst-70 has been identified to be an active and stable catalyst with sufficient acidity to couple C9-alkenes. The inhibiting effect of water on alkene oligomerization can be minimized, because C9 alkenes derived from aqueous solutions of GVL separate spontaneously from water. The effect of other impurities arising from the cascade process for production of C9 alkenes from GVL, such as 5-nonanone and 5-nonanol, has been studied. Ketones are shown to be inert, while alcohols readily dehydrate on acid sites, producing an equivalent of water, which inhibits the rate of oligomerization. Small amounts of 5-nonanol present with C9-alkenes (< 1%) have a promotional effect, due to swelling of the catalyst by polar molecules; however, large amounts of 5-nonanol lead to inhibition of oligomerization. Other more reactive alkenes present in C9-alkenes produced from GVL, such as hexene and heptene isomers, compete for acid sites with the nonene feed. These smaller, more reactive alkenes are readily coupled at high conversion. Accordingly, with this process approximately 50 kg of liquid hydrocarbons can be produced from 100 kg of GVL retaining more than 90% of its energy content.
URL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_________::27e8bcf47fb4c4f8b9482656987b39f9
https://doi.org/10.1039/c001899f
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