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Fermented 2-methyl-1-propanol (isobutanol) can be used directly as a biofuel or can be catalytically dehydrated to 2-methylpropene (isobutylene), which serves as a platform molecule for synthesizing other fuels or chemicals. The dehydration reaction was studied over alumina catalysts to determine the impact of process conditions and model compound impurities from fermentation. No significant impurity effects were observed over short (8 h) timescales and dehydration was demonstrated at high conversion and with high selectivity to isobutylene.

Cetane number improvement of diesel fuels is a difficult task that refiners will face in the near future. Aromatics saturation by deep hydrogenation is a necessary, but perhaps not sufficient step in the diesel treatment. Some researchers have proposed selective ring opening (SRO) as an additional step in the upgrading. In this work, we explore some possible reaction pathways of compounds typically found in diesel after different levels of hydrogenation, i.e. decalin (decahydronaphthalene), perhydrophenanthrene, tetralin (1,2,3,4-tetrahydronapthalene), as well as 1-ring and 2-ring aromatic phenanthrenes. We have estimated the cetane number (CN) of each individual compound involved in the reaction pathways, using an artificial neural network program that was trained with pure compound cetane numbers from a database. The results demonstrate the great challenge that reaching high CN represents. In the conversion of decalin, acidic catalysts alone are not able to yield products with CN significantly higher than the decalin feed. Similarly, no significant gain in CN can be expected with hydrogenolysis metal catalysts operating via the dicarbene mechanism. Only in the case of selective metal-catalyzed hydrogenolysis, with preferential cleavage at substituted C–C bonds, the predicted products have CN substantially higher than the decalin feed. As expected, branching has a strongly negative effect on the CN and it should be minimized. Both, metal-catalyzed di-carbenium C–C cleavage and acid-catalyzed ring contraction/ring opening combination leave branching groups in the product. Similarly, the acid-catalyzed ring opening of perhydrophenanthrene does not result in a significantly higher CN than the initial feed. The possibility of minimizing hydrogen consumption in the CN improvement process by an initial partial hydrogenation followed by ring opening was tested by using phenanthrene and tetralin as probe molecules. In the first reaction strategy, partially hydrogenated phenanthrenes (1-ring and 2-ring aromatics) were followed by ring opening of one of the saturated rings. Although this option would lead to lower overall hydrogen consumption, it results in products of much lower CNs than the ones obtained by full hydrogenation of phenanthrene. Similar results are obtained for tetralin. From this analysis, it is clear that upgrading CN of diesel requires extensive hydrogen consumption. For further upgrading, highly selective hydrogenolysis catalysts are needed in order to minimize branching and therefore obtain high CN products.

From the beginning of supercritical water oxidation (SCWO) research in the early 1980s, mathematical models have been used to correlate, predict, and explain experimental reaction kinetic data. Initially, these were simple global rate laws, involving only a single overall reaction or a few reactions, each with its own arbitrary rate law. As computational power increased and the library of elementary reactions from the combustion literature grew, it became feasible to construct elementary reaction rate models, which are a more accurate means of representing the SCWO process. Early efforts to construct elementary reaction rate models resulted in very poor agreement with experimental data unless model parameters were adjusted to optimize the fit. However, today with considerably more computing power and a more robust collection of elementary rate parameters from the combustion literature, rate predictions in the relatively low-temperature, high-pressure SCWO environment are more effective and accura...

In this paper, we explore the efficacy of (1) reducing the iodine value of soy-derived biodiesel fuels through increasing the methyl oleate (methyl ester of oleic acid) content and (2) addition of cetane improvers, as strategies to combat the biodiesel NOx effect: the increase in NOx emissions observed in most studies of biodiesel and biodiesel blends. This is accomplished by spiking a conventional soy-derived biodiesel fuel with methyl oleate or with cetane improver. The impact on bulk modulus of compressibility, fuel injection timing, cetane number, combustion, and emissions were examined. The conventional B20 blend produced a NOx increase of 3–5% relative to petroleum diesel, depending on injection timing. However, by using a B20 blend where the biodiesel portion contained 76% methyl oleate, the biodiesel NOx effect was eliminated and a NOx neutral blend was produced. The bulk modulus of petroleum diesel was measured to be 2% lower than B20, yielding a shift in fuel injection timing of 0.1–0.3 crank angle. The bulk modulus of the high methyl oleate B20 blend was measured to be 0.5% lower than B20, not enough to have a measurable impact on fuel injection timing. Increasing the methyl oleate portion of the biodiesel to 76% also had the effect of increasing the cetane number from 48.2 for conventional B20 to 50.4, but this effect is small compared to the increase to 53.5 achieved by adding 1000 ppm of 2-ethylhexyl nitrate (EHN) to B20. For the particular engine tested, NOx emissions were found to be insensitive to ignition delay, maximum cylinder temperature, and maximum rate of heat release. The dominant effect on NOx emissions was the timing of the combustion process, initiated by the start of injection, and propagated through the timing of maximum heat release rate and maximum temperature.

The effect of catalyst temperature on the partial oxidation reaction pathways of methane over platinum is investigated in a stagnation-flow reactor. A new experimental method is described that uses Raman spectroscopy to measure the concentration of CH 4 along the centerline of the reactor with the Pt surface at 900-1100 °C. The method permits the direct comparison of the measured reactivity with that predicted by the CHEMKIN SPIN stagnation-flow code when combined with recently developed partial oxidation elementary reaction mechanisms. A significant increase in the reactivity of CH 4 on Pt is observed between 1000 and 1100 °C, concurrent with an increase in the selectivity to H 2 and CO. No single mechanism available in the literature correctly models the increase in reactivity or the change in selectivity in this temperature range. The experimental results are interpreted by examining the competitive adsorption between CH 4 and O 2 and the two pathways by which CH 4 can undergo dissociative adsorption. The temperature dependence of the sticking coefficient for the direct dissociative adsorption of CH 4 is specifically identified as an important yet highly uncertain parameter in the reaction mechanism.

Experiments were conducted to investigate the reforming of organic compounds (primarily methanol) in supercritical water at 550–700°C and 27.6 MPa in a tubular Inconel 625 reactor. The results show that methanol can be completely converted to a product stream that is low in methane and near the equilibrium composition of hydrogen, carbon monoxide, and carbon dioxide. The effect of reactor temperature, feed concentration of methanol, and residence time on both conversion and product gas composition was investigated and the results are presented. Reaction pathways and potential applications of this technology are discussed. Ethanol and ethylene glycol resulted in less desirable effluent gas, with high concentrations of methane and carbon monoxide. Acetone and diesel fuel both resulted in the reactor becoming plugged.

Oxidation and hydrolysis experiments with ethanol were investigated in supercritical water using a lab-scale, plug-flow reactor system at temperatures from 433 to 494 °C and a fixed pressure of 246 bar. The residence times ranged from 2 to 12 s, and the initial concentration of ethanol was set to 1 mmol l −1 . In the hydrolysis experiments, ethanol did not react to a significant degree relative to the conversions observed in oxidation experiments. The conversion for the hydrolysis experiments was between 1.9 and 7.4%. In the oxidation experiments, the initial oxygen concentration was set to 3 mmol l −1 , according to the stoichiometric ratio for complete mineralization. The major products of the reaction were acetaldehyde and formaldehyde in the liquid phase and carbon monoxide and carbon dioxide in the gas phase. An assumed first-order global rate expression was determined with an activation energy of 163.9±3.3 kJ mol −1 and a pre-exponential factor of 10 11.1±4.5 to a 95% confidence level. An induction time was experimentally observed, ranging from 0.5 to 3.8 s, with longer times corresponding to lower temperatures. A second set of experiments was performed to investigate the dependence of the reaction rate on oxygen concentration. The fuel equivalence ratio was varied from 0.5 to 1.9. Experiments were conducted at residence times of 2.5 and 3.0 s at 470 °C and 246 bar. A global rate expression was regressed for the ethanol reaction rate from the complete set of data. The resulting pre-exponential factor was 10 17.23±1.65 ; the activation energy was 213.9±18.3 kJ mol −1 ; and the reaction orders for ethanol and oxygen were 1.34±0.11 and 0.55±0.19, respectively.

Two decomposition mechanisms for methyl tert-butyl ether (MTBE) under hydrothermal conditions were analyzed: a unimolecular decomposition pathway and an acid-catalyzed hydrolysis pathway. Ab initi...

Experiments were conducted to measure the isothermal rate of methyl tert-butyl ether (MTBE) decomposition in water at hydrothermal conditions (T = 150−600 °C and P = 250 bar). The primary identified products of the reaction of MTBE were methanol, isobutene, and tert-butyl alcohol. An assumed first-order rate constant for the hydrolysis of MTBE was determined at each temperature and showed a local maximum below the critical temperature of water (374 °C) followed by a local minimum above it. This behavior was modeled using an acid-catalyzed mechanism, which resulted in a rate expression with a first-order dependence on the concentration of H+. Because of the dramatic decrease in the ion dissociation constant of water (Kw) in the critical region, the drop in the rate of reaction could be modeled quantitatively over the entire temperature range.

Methylene chloride (CH{sub 2}Cl{sub 2}) is a representative model compound commonly found in aqueous wastes, process effluents, and contaminated soils and sediments. Oxidation in supercritical water provides a viable treatment and remediation pathway to convert CH{sub 2}Cl{sub 2} to CO{sub 2}, H{sub 2}O, and HCI. However, in earlier work, partial hydrolysis was observed at subcritical temperatures ({lt}374 C). This low-temperature reactivity complicates the measurement of kinetic data. In this study, the kinetics of CH{sub 2}Cl{sub 2} hydrolysis in sub- and supercritical water were experimentally measured and modeled. Catalytic effects from a high nickel content alloy used for the reactor were studied by comparing kinetic data obtained in quartz ampoules with and without metal presents. No heterogeneous catalysis effects were observed. Reaction rates from 100 to 500 C were measured to check the reproducibility of existing published data (up to 150 C) and to extend the database for hydrolysis to the supercritical region in order to develop a robust empirical global rate expression. The data show a local maximum in the rate constant below the critical point of water, consistent with a possible change in the reaction mechanism induced by changes in the solvent's physical properties (dielectric constant, density, etc.). Variationsmore » in the global rate constant agree quantitatively with predictions obtained by applying the Kirkwood model, which accounts for changes in the dielectric constant and density of the solvent.« less

We provide new or revised vibrational assignments for three hydrofluorocarbons (HFCs) and one hydrochlorofluorocarbon (HCFC) through the combined use of experimental absolute infrared intensity measurements, experimental Raman measurements and ab initio computations of vibrational frequencies, absolute infrared intensities, and Raman intensities. CHF 2 CH 3 (HFC-152a), CF 3 CH 3 (HFC-143a), CF 3 CHF 2 (HFC-125), and CHCl 2 CF 3 (HCFC-123) are the molecules investigated in this study. We have measured the vapor infrared spectra from 400 to 4000 cm −1 at a resolution (0.08 cm −1 ) sufficient to resolve some overlapping fundamentals and to assign symmetry species for several bands on the basis of their rotational band contours and absolute infrared intensities. Raman spectra were measured for the HFCs at pressures between 3.8 and 11.1 atm and for HCFC-123 in the liquid phase. Second-order Moller–Plessett (MP2) level of theory and the 6-31G** basis set were used to optimize molecular geometry and calculate harmonic vibrational frequencies and infrared intensities; Hartree Fock (HF) level of theory was used to calculate Raman intensities. The higher-resolution infrared spectra and experimental absolute infrared intensities, the Raman spectra and relative Raman intensities, together with the results of the computations, allow a firm assignment of previously ambiguous bands. On the basis of the current assignments, we find that the scaled MP2/6-31G** frequencies are in good agreement with the observed frequencies. Furthermore, the calculated absolute infrared intensities and calculated Raman intensities are generally in good agreement with the experimental measurements.

ASME Internal Combustion Engine Division 2006 Fall Technical Conference : Sacramento, CA, November 5-8, 2006, available, unlimited, public, Series: Track 2: Fuels and Combustion. Session: 2-1 HCCI and Advanced Combustion

In this paper, cyclic variations in the combustion process of a single-cylinder HCCI engine operated with n-heptane were measured over a range of intake air temperatures and pressures, compression ratios, air/fuel ratios, and exhaust gas recirculation (EGR) rates. The operating conditions produced a wide range of combustion timings from overly advanced combustion where knocking occurred to retarded combustion where incomplete combustion was detected. Cycle-to-cycle variations were shown to depend strongly on the crank angle phasing of 50% heat release and fuel flow rate. Combustion instability increased significantly with retarded combustion phasing especially when the fuel flow rate was low. Retarded combustion phasing can be tolerated when the fuel flow rate is high. It was also concluded that the cyclic variations in imep are primarily due to the variations in the total heat released from cycle-to-cycle. The completeness of the combustion process in one cycle affects the in-cylinder conditions and resultant heat release in the next engine cycle.Copyright © 2007 by ASME and National Research Council of Canada