Hydrogenation of Hydrocarbons through Partial Oxidation in Supercritical Water (original) (raw)
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Fuel and Energy Abstracts, 2011
Continuous supercritical water gasification of isooctane, a model gasoline compound, is investigated using an updraft gasification system. A new reactor material, Haynes Ò 230 Ò alloy, is employed to run gasification reactions at high temperature and pressure (763 AE 2 C; 25 MPa). A large-volume reactor is used (170 mL) to enable the gasification to be run at a long residence time, up to 120 s. Various gasification experiments are performed by changing the residence time (60e120 s), the isooctane concentration (6.3e14.7 wt%), and the oxidant concentration (equivalent oxidant ratio 0e0.3). The total gas yield and the hydrogen gas yield increase with increasing residence time. At 106 s and an isooctane concentration of 6.3 wt%, a very high hydrogen gas yield of 12.4 mol/mol isooctane, which is 50% of the theoretical maximum hydrogen gas yield and 92% of the equilibrium hydrogen gas yield under the given conditions, is achieved. Under these conditions, supercritical water partial oxidation does not increase the hydrogen gas yield significantly.
Chemical Engineering Research and Design, 2014
Continuous supercritical water gasification (SCWG) of various feedstocks of C1-C16 was conducted to produce hydrogen-rich gas. These feedstocks represent model compounds of biomass such as methanol/ethanol (alcoholtype), glucose and glycerol (byproducts of biodiesel synthesis), and model compounds of petroleum fuels such as iso-octane/n-octane (gasoline), n-decane/n-dodecane (jet fuels) and n-hexadecane (diesel). Almost complete gasification of all the feedstocks was achieved at 25 MPa, 740 • C and 10 wt% with low total organic carbon values of their liquid effluents. The hydrogen gas yields of each feedstock were very similar to the theoretical equilibrium yields estimated by Gibbs free energy minimization. SCWG at different gasification temperatures (650 and 740 • C) and concentrations (10 and 20 wt%) revealed that methanol and ethanol (alcohols), the simple oxygenated hydrocarbons, were easier to be gasified, producing negligible amounts of liquid products, when compared with long-chain hydrocarbons (iso-octane and n-decane) under the identical conditions. When the feedstock concentration was increased from 10 to 20 wt%, the equilibrium hydrogen ratio from iso-octane gasification decreased from 1.02 to 0.79 while that of n-decane increased from 1.12 to 1.50, implying that a branched hydrocarbon may be more resistant to gasification in supercritical water.
Catalytic gasification of light and heavy gas oils in supercritical water
Journal of the Energy Institute, 2020
Canada has the third-largest oil sand reserves in the world as a result of which, it generates considerable amounts of light gas oil and heavy gas oil through petroleum distillation. With the escalating energy demands, it has become essential to explore alternative fuel resources from biomass and petrochemical residues. This study explores the potential of supercritical water gasification to transform light and heavy gas oils to hydrogen-rich syngas through the optimization of process conditions such as temperature (375e675 C), feed concentration (20e35 wt%) and reaction time (30e75 min). Nickel-supported functionalized carbon nanotubes (10%Ni/FCNT) were synthesized for application in catalytic supercritical water gasification. The functionalization of carbon nanotubes resulted in an increase in their surface area from 108 m 2 /g (in pristine CNT) to 127 m 2 /g (in FCNT) and 122 m 2 /g (in 10%Ni/FCNT). The impregnation of catalytic nickel particles onto carbon nanotubes was confirmed through X-ray diffraction (XDR) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Fouriertransform infrared (FTIR) spectroscopy of both gas oils revealed the presence of aliphatics, alkyl-aryl ethers and sulfur-containing compounds among several other aromatics. Light gas oil revealed higher hydrogen yields of 3.32 mol/kg compared to that of heavy gas oil (2.79 mol/kg) at optimal process conditions, i.e. 675 C and 75 min, 20 wt% feed concentration. However, 10%Ni/FCNT enhanced hydrogen yields (4.46 mol/kg), total gas yield (9.22 mol/kg), hydrogen selectivity (94%) and lower heating value (1685 MJ/kg) of product gases obtained from light gas oil in contrast to heavy gas oil. This study indicates a tremendous potential of gas oils for hydrogen generation via hydrothermal gasification.
Catalytic partial oxidation of methane in supercritical water
The Journal of Supercritical Fluids, 1994
Partial oxidation of methane under supercritical water environment at 658 K and 26 MPa using a batch reactor was examined in the presence of metal oxide catalysts and H 2 O 2 as a molecular oxygen source. Within a parameter space of feed concentrations (CH 4 /H 2 O and O 2 /CH 4 ratios), there existed a domain that gave high C 2 + hydrocarbon yield reaching to ca. 4 %. Obtained products were a mixture of hydrocarbons up to C 4 with ethane as a major component, accompanied with CO, CO 2 , H 2 and methanol. The domain that gave high hydrocarbon yield did not coincide with that which gave high methanol yield. Catalyst survey indicated that transition metal oxides are effective for the production of C 2 + hydrocarbons under the present conditions. In view of the oxidative coupling of methane in all reaction modes explored previously, presently reported level of hydrocarbon yield is unprecedented at this low reaction temperature.
Catalysts
The generation of hydrogen from unconventional oil is expected to increase significantly during the next decade. It is commonly known that hydrogen is an environmentally friendly alternative fuel, and its production would partially cover the gap in energy market requirements. However, developing new cheap catalysts for its production from crude oil is still a challenging area in the field of petroleum and the petrochemical industry. This study presents a new approach to synthesizing and applying promising catalysts based on Ni, Co, and Ni-Co alloys that are supported by aluminum oxide Al2O3 in the production of hydrogen from extra-heavy crude oil in the Tahe Oil Field (China), in the presence of supercritical water (SCW). The obtained catalysts were characterized via scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, transmission electron microscopy (TEM), and, X-ray diffraction analysis (XRD). The obtained XRD data showed 3.22% of Co2+ in the Co...
Hydrogen production from 2-propanol over Pt/Al2O3 and Ru/Al2O3 catalysts in supercritical water
International Journal of Hydrogen Energy, 2013
One of the alternative energy sources to fossil fuels is the use of hydrogen as an energy carrier, which provides zero emission of pollutants and high-energy efficiency when used in fuel cells, hydrogen internal combustion engines (HICE) or hydrogen-blend gaseous fueled internal combustion engines (HBICE). The gasification of organics in supercritical water is a promising method for the direct production of hydrogen at high pressures, with very short reaction times. In this study, hydrogen production from 2-propanol over Pt/Al 2 O 3 and Ru/Al 2 O 3 catalysts was investigated in supercritical water. To investigate the influences on hydrogen production, the experiments were carried out in the temperature range of 400 e550 C and in the reaction time range of 10e30 s, under a pressure of 25 MPa. In addition, different 2-propanol concentrations and reaction pressures were tested in order to comprehend the effects on the gasification yield and hydrogen production. It was found that Pt/Al 2 O 3 catalyst was much more selective and effective for hydrogen production when compared to Ru/Al 2 O 3. During the catalytic gasification of a 0.5 M solution of 2-propanol, a hydrogen content up to 96 mol% for a gasification yield of 5 L/L feed was obtained.
Upgrading and desulfurization of heavy oils by supercritical water
The Journal of Supercritical Fluids, 2015
Supercritical water upgrading (SCWU) of heavy oils reduces sulfur content and decreases average molecular weight, without rejecting carbon as coke products. Despite many years of industrial and academic scrutiny, many fundamental questions remain in the field: intrinsic reaction rates and mechanisms; the role of water; the need for catalysts; the importance of phase behavior and mixing. In 2009, MIT initiated a SCWU research program aimed at improving the understanding of the relevant physical, chemical, and catalytic phenomena. This overview summarizes the work performed at MIT within the historical context of SCWU with a particular focus on new kinetic rate measurements and modeling, reaction mechanism analysis, catalyst investigation, and combined mass/heat transport modeling of hydrocarbon/water mixtures. Kinetic rate measurements showed that sulfide decomposition during SCWU is consistent with a radical chain reaction pathway. Mechanistic studies and product distribution analysis identified that sulfide decomposition likely occurs via thioaldehyde and aldehyde intermediates and that water plays important roles in thioaldehyde hydrolysis (as a reactant) and aldehyde decarbonylation (as a catalyst). Catalytic investigation found that ZnO has potential to improve sulfur removal during SCWU, without addition of molecular hydrogen. Mixing studies revealed the complex dynamic processes that occur when hydrocarbons are injected into near or supercritical water. The article concludes with a summary of research needs and thoughts on the future of SCWU.
Gasification Pathways and Reaction Mechanisms of Primary Alcohols in Supercritical Water
Supercritical water gasification is a promising waste-to-energy technology with the ability to convert aqueous and/or heterogeneous organic feedstocks to high-value gaseous products, e.g., green hydrogen. Reaction behavior of complex molecules in supercritical water can be inferred through knowledge of the reaction pathways of model compounds in supercritical water. In this study methanol, ethanol, and isopropyl alcohol are gasified in a continuous supercritical water reactor at temperatures between 500 and 560 °C, and for residence times between 3 and 8 s. In situ Raman spectroscopy is used to rapidly identify and quantify reaction products. The experiments confirm the dominance of chain-branching, free radical reaction mechanisms that are responsible for decomposing primary alcohols in the supercritical water environment. Reaction pathways and mechanisms for three alcohols are proposed, conversion metrics are presented, and results are compared with known reaction mechanisms for m...
STEPPING STONES TOWARD OXIDATION PROCESSES IN SUPERCRITICAL WATER
Under supercritical conditions (i.e. when the temperature and the pressure of a substance are above its thermodynamic critical point), water becomes a fluid with unique properties that can be used to treat a wide variety of wastes. For example, during Supercritical Water Oxidation (SCWO) organic wastes can be almost fully converted into carbon dioxide and water. Already used in a variety of terrestrial applications (for example onboard ships), SCWO technology, because of its potential for extremely high waste conversion efficiencies, is of great interest in the context of space exploration programs. A SCWO reactor could be used in the treatment of a number of waste streams typically found onboard spacecraft used in long duration missions or as a part of the Environmental Control and Life Support (ECLS) system for an extraterrestrial habitat. As part of the DECLIC program, the first two investigation phases motivated by the potential of future SCWO applications in microgravity have e...