Charles E. Taylor

Formation and dissociation studies for optimizing the uptake of methane by methane hydrates

Abstract Characteristics such as temperature and pressure profiles for methane hydrate formation and dissociation in pure water, simulated seawater, and water–surfactant systems have been established. A hysteresis effect has been observed for repeated formation–dissociation cycles of the same methane–water system. In an attempt to maximize the uptake of methane during methane hydrate formation, the addition of sodium dodecyl sulfate provided methane uptake of over 97% of the theoretical maximum uptake. Additional surfactants were tested for their ability to enhance the uptake of methane for hydrate formation. Successful demonstration of efficient methane storage using hydrate formation enhanced by addition of surfactants could provide a safe, low-cost alternative method for storage of natural gas at remote locations.

Molecular-dynamics simulations of methane hydrate dissociation

Nonequilibrium molecular-dynamics simulations have been carried out at 276.65 K and 68 bar for the dissolution of spherical methane hydrate crystallites surrounded by a liquid phase. The liquid was composed of pure water or a water-methane mixture ranging in methane composition from 50% to 100% of the corresponding theoretical maximum for the hydrate and ranged in size from about 1600 to 2200 water molecules. Four different crystallites ranging in size from 115 to 230 water molecules were used in the two-phase systems; the nanocrystals were either empty or had a methane occupation from 80% to 100% of the theoretical maximum. The crystal-liquid systems were prepared in two distinct ways, involving constrained melting of a bulk hydrate system or implantation of the crystallite into a separate liquid phase. The breakup rates were very similar for the four different crystal sizes investigated. The method of system preparation was not found to affect the eventual dissociation rates, despite a lag time of approximately 70 ps associated with relaxation of the liquid interfacial layer in the constrained melting approach. The dissolution rates were not affected substantially by methane occupation of the hydrate phase in the 80%-100% range. In contrast, empty hydrate clusters were found to break up significantly more quickly. Our simulations indicate that the diffusion of methane molecules to the surrounding liquid layer from the crystal surface appears to be the rate-controlling step in hydrate breakup. Increasing the size of the liquid phase was found to reduce the initial delay in breakup. We have compared breakup rates computed using different long-range electrostatic methods. Use of the Ewald, minimum image, and spherical cut-off techniques led to more rapid dissociation relative to the Lekner method.

New developments in the photocatalytic conversion of methane to methanol

Abstract Investigation of direct conversion of methane to transportation fuels has been an on-going effort at FETC for over 14 years. One of our current areas of research is the conversion of methane to methanol, under mild conditions, using light, water, and a semiconductor photocatalyst. Research in our laboratory is directed toward adapting the chemistry developed for photolysis of water to that of methane conversion. The reaction sequence of interest uses visible light, a doped tungsten oxide photocatalyst and an electron transfer molecule to produce a hydroxyl radical. Hydroxyl radical can then react with a methane molecule to produce a methyl radical. In the preferred reaction pathway, the methyl radical then reacts with an additional water molecule to produce methanol and hydrogen.

Direct Conversion of Methane to Liquid Hydrocarbons Through Chlorocarbon Intermediates

Abstract The chemical activation of methane and its subsequent conversion to oxygenates or higher hydrocarbons have been the objects of intensive research in the past several years. At the Pittsburgh Energy Technology Center, a novel combination of two existing process concepts has been examined and appears capable of producing higher hydrocarbons from methane with high yield and selectivity. Methane, oxygen, and hydrogen chloride are reacted over an oxyhydrochlorination catalyst in the first stage to produce methyl chloride and water. In the second stage, the methyl chloride is converted to higher hydrocarbons, namely paraffins, olefins, aromatics, and cycloparaffins, over a zeolite, such as ZSM-5. In the process concept described, the final hydrocarbon mixture is largely in the gasoline (C 4 , C 10 ) boiling range.

Conversion of substituted methanes over ZSM-catalysts

Publisher Summary Methanol and chloromethane reacted under identical conditions over ZSM-5 and ZSM-11 catalysts to produced similar product streams. The conversion of reactants over ZSM-5 catalysts is high (>99.7%) even after extended periods of time on stream. Chloromethane reaction over the ZSM-11 catalysts causes a more rapid deactivation than that observed for methanol conversion. Exposure of the ZSM-5 and ZSM-11 catalysts at elevated temperatures (∼550˚C) to air removes the accumulated coke on the catalyst and returns the conversions and product selectivities to values observed for pristine catalysts.

Photocatalytic conversion of methane

Investigation of the direct conversion of methane to transportation fuels has been an ongoing effort at PETC for over 10 years. One of our current areas of research is the conversion of methane to methanol under mild conditions using light, water, and a semiconductor photocatalyst. The use of three relatively abundant and inexpensive reactants, light, water, and methane, to produce methanol is attractive. Research in our laboratory is directed toward applying techniques developed for the photochemical splitting of water to methane conversion. The reaction sequence of interest initially produces a hydroxyl radical with the aid of a doped tungsten oxide photocatalyst and an electron transfer molecule. Hydroxyl radical can then react with a methane molecule to produce a methyl radical. In the preferred reaction pathway, the methyl radical then reacts with an additional water molecule to produce methanol and hydrogen.

Activation of methane with organopalladium complexes

Abstract Selective, direct oxidation of methane to methanol is a process of scientific interest and industrial importance. Reports have appeared in the literature describing the use of organometallic complexes to effect this transformation [1–5]. Investigation of one of these reaction schemes in our laboratory has produced interesting results. Our research effort was an extension of work reported by Sen et al. [3]. The reported reaction occurs between methane (at 800 psig 5.52 MPa) and palladium(II) acetate in trifluoroacetic acid at 80°C (Eq. (1)). The product, methyl trifluoroacetate, is readily hydrolyzed to produce methanol and trifluoroacetic acid. It is reported that methyl trifluoroacetate is produced with reported conversions, calculated on palladium metal recovery, of ∼ 60 percent. CH 4 + Pd(O 2 CCH 3 ) 2 → 80° C , 800 PSIG CF 3 COOH CF 3 CO 2 CH 3 + Pd .

Photocatalytic production of methanol and hydrogen from methane and water

Abstract Investigation of direct conversion of methane to transportation fuels has been an ongoing effort at PETC for over 10 years. One of our current areas of research is the conversion of methane to methanol, under mild conditions, using light, water, and a semiconductor photocatalyst. Research in our laboratory is directed toward adapting the chemistry developed for photolysis of water to that of methane conversion. The reaction sequence of interest uses visible light, a doped tungsten oxide photocatalyst and an electron transfer molecule to produce a hydroxyl radical. Hydroxyl radical can then react with a methane molecule to produce a methyl radical. In the preferred reaction pathway, the methyl radical then reacts with an additional water molecule to produce methanol and hydrogen.

Novel Techniques for the Conversion of Methane Hydrates

Abstract While methane hydrates hold promise as an energy source, methods for the economical recovery of methane from the hydrate must be developed. Effective means of converting the natural gas into a more useful form, such as the photocatalytic oxidation of methane to methanol, may address some of the needs for methane recovery and use. Methanol retains much of the original energy of the methane, and is a liquid at room temperature, which alleviates some of the concerns about fuel transportation and storage. Desired characteristics of the natural gas conversion process include selectivity toward methanol formation, efficiency of conversion, low cost, and ease of use of the conversion method. A method for the conversion of methane to methanol involving a photocatalyst, light, and an electron transfer molecule, is described. Moreover, novel use of the formation of a methane hydrate as a means of maximizing the levels of methane in water, as well as providing the reactants in close proximity, is described. This method demonstrated successful conversion of methane contained in a methane hydrate to methanol.

Reduction of CO2 in Steam Using a Photocatalytic Process to Form Formic Acid

The role that CO2 potentially plays in global climate change has prompted many researchers to study effective methods for converting it into useful raw materials. However, due to the barrier that the thermal stability of the CO2 molecule presents for effective conversion reactions, catalytic processes must often be used to afford efficient conversions. This work evaluates a photocatalytic process for the conversion of CO2 into formic acid. Using a sol-gel titania photocatalyst, light energy, and steam, CO2 is converted into formic acid inside a custom quartz conversion apparatus. Advantages to this conversion include the use of inexpensive and abundant reactants, light, water, and CO2, as well as potentially providing a mitigating technology for CO2 sequestration. Results for the conversion process are presented, and comments on the efficiency of the system under study, as well as a proposed photocatalytic material for future CO2 conversion research, are given.