For the first time, high surface area nanofibers were synthesized using aluminum isopropoxide monomer with acetic acid as the polycondensation agent in the green solvent, supercritical carbon dioxide (scCO(2)). It was found that the synthesis temperature, pressure, concentration, and acid/alkoxide ratio had a large effect on fiber formation. By optimizing the experimental conditions at 80 degrees C and 6000 psi of scCO(2) using aluminum isopropoxide at a concentration of 0.3 mmol/mL and acid/alkoxide ratio of 10, alumina nanofibers were formed ranging from 11 to 22 nm in diameter and 500 to 1000 nm in length, and with surface areas up to 580 m(2)/g. Lower temperatures gave irregular shaped nanoparticles, while a lower acid/alkoxide ratio (5:1) resulted in the formation of low surface area alumina bars. Increasing pressure led to better separation of the nanofibers and higher surface areas. In addition to the synthesis conditions, the influence of calcination temperature on the structural, textural, and morphological properties of the materials was examined using various physicochemical techniques including electron microscopy, TGA/DTA, powder XRD, FTIR, XPS, and nitrogen adsorption/desorption analysis. The long fibers with high aspect ratios were found to be thermally stable even after calcining at up to 1050 degrees C. The mechanism of fiber formation in scCO(2) is proposed based on a [Al(OH)(CH(3)CO(2))(2)](n) polycondensate backbone.

No abstract

No abstract

In this study, we report a single-step continuous production of straight-chain liquid hydrocarbons from oleic acid and other fatty acid derivatives of interest including castor oil, frying oil, and palm oil using Mo, MgO, and Ni on Al 2 O 3 as catalysts in subcritical water. Straight-chain hydrocarbons were obtained via decarboxylation and hydrogenation reactions with no added hydrogen. Mo/Al 2 O 3 catalyst was found to exhibit a higher degree of decarboxylation (92%) and liquid yield (71%) compared to the other two examined catalysts (MgO/Al 2 O 3 , Ni/Al 2 O 3 ) at the maximized conditions of 375 °C, 4 h of space time, and a volume ratio of 5:1 of water to oleic acid. The obtained liquid product has a similar density (0.85 kg/m 3 at 15.6 °C) and high heating value (44.7 MJ/kg) as commercial fuels including kerosene (0.78–0.82 kg/m 3 and 46.2 MJ/kg), jet fuel (0.78–0.84 kg/m 3 and 43.5 MJ/kg), and diesel fuel (0.80–0.96 kg/m 3 and 44.8 MJ/kg). The reaction conditions including temperature, volume ratio of water-to-feed, and space time were maximized for the Mo/Al 2 O 3 catalyst. Characterization of the spent catalysts showed that a significant amount of amorphous carbon deposited on the catalyst could be removed by simple carbon burning in air with the catalyst recycled and reused.

Current interest in renewable fuel production is focused on high-performance fuels such as jet fuel because of their premium value in the marketplace. Currently, lower-value fuels such as biodiesel can be obtained using a variety of feedstocks, but contain significant amounts of oxygen, hence lowering their fuel value. In this work, we examined a one-pot catalytic hydrothermal process for the decarboxylation with an activated carbon catalyst of oleic acid as a model compound for free fatty acids. Temperature (350–400 °C), water-to-oleic acid ratio (2:1–4:1, v/v), catalyst, catalyst-to-total feed ratio (0.15–0.75), and residence time (1–2 h) were found to be key factors for removing oxygen from oleic acid. The complete removal of the carboxylic group from the upgraded liquid phase was achieved at 400 °C with a water-to-oleic acid ratio of 4:1 (v/v) and a residence time of 2 h as confirmed by FTIR and 13C NMR results. The pseudo-first-order reaction rate constant was found to follow Arrhenius behavior with the activation energy determined to be 90.6 ± 3 kJ/mol. GC-FID results showed a high selectivity to heptadecane conversion, whereas the GC-TCD results indicated that decarboxylation was the dominating chemical reaction. High heating values and fuel densities in the range of commercial jet fuels were obtained using this approach without the addition of high-pressure hydrogen or a hydrogen-donor solvent.