Dirk D. Link

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.

Recent developments in the production of liquid fuels via catalytic conversion of microalgae: experiments and simulations

Due to continuing high demand, depletion of non-renewable resources and increasing concerns about climate change, the use of fossil fuel-derived transportation fuels faces relentless challenges both from a world markets and an environmental perspective. The production of renewable transportation fuel from microalgae continues to attract much attention because of its potential for fast growth rates, high oil content, ability to grow in unconventional scenarios, and inherent carbon neutrality. Moreover, the use of microalgae would minimize “food versus fuel” concerns associated with several biomass strategies, as microalgae do not compete with food crops in the food chain. This paper reviews the progress of recent research on the production of transportation fuels via homogeneous and heterogeneous catalytic conversions of microalgae. This review also describes the development of tools that may allow for a more fundamental understanding of catalyst selection and conversion processes using computational modelling. The catalytic conversion reaction pathways that have been investigated are fully discussed based on both experimental and theoretical approaches. Finally, this work makes several projections for the potential of various thermocatalytic pathways to produce alternative transportation fuels from algae, and identifies key areas where the authors feel that computational modelling should be directed to elucidate key information to optimize the process.

Improved benzene production from methane dehydroaromatization over Mo/HZSM-5 catalysts via hydrogen-permselective palladium membrane reactors

The effectiveness of hydrogen-permselective palladium membrane reactors for non-oxidative methane dehydroaromatization (MDA) over 4 wt% Mo/HZSM-5 catalysts was investigated as a function of weight hourly space velocity (WHSV) at 700 °C and atmospheric pressure. CH4 conversion and aromatic product yield decrease with increasing WHSV from 750 to 9000 cm3 gcat−1 h−1. C6H6 is the main C-containing product at and below 3000 cm3 gcat−1 h−1 whereas C2H4 dominates the C-product distribution at higher WHSVs. Due to selective removal of H2 from the reaction products in catalytic membrane reactors, C6H6 yield is significantly improved over the whole WHSV range compared to those obtained in fixed-bed reactors. H2 recovery is strongly influenced by WHSV as it decreases from 48.3% at 750 cm3 gcat−1 h−1 to 6.8% at 9000 cm3 gcat−1 h−1. There exists a trade-off between catalytic activity and H2 recovery, which results in the maximum enhancement (~360%) in C6H6 yield at 3000 cm3 gcat−1 h−1. At this intermediate space velocity, the largest concentration of H2 is found in the retentate stream and helps alleviate coke accumulation particularly on HZSM-5. Carbon is deposited on the inner surface of the membrane reactor portion in contact with the catalyst bed and transports to the outer surface, thus causing H2 permeability to decrease over the 15 h reaction period.

Determination of Free Fatty Acids and Triglycerides by Gas Chromatography Using Selective Esterification Reactions

A method for selectively determining both free fatty acids (FFA) and triacylglycerides (TAGs) in biological oils was investigated and optimized using gas chromatography after esterification of the target species to their corresponding fatty acid methyl esters (FAMEs). The method used acid catalyzed esterification in methanolic solutions under conditions of varying severity to achieve complete conversion of more reactive FFAs while preserving the concentration of TAGs. Complete conversion of both free acids and glycerides to corresponding FAMEs was found to require more rigorous reaction conditions involving heating to 120°C for up to 2 h. Method validation was provided using gas chromatography-flame ionization detection, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry. The method improves on existing methods because it allows the total esterified lipid to be broken down by FAMEs contributed by FFA compared to FAMEs from both FFA and TAGs. Single and mixed-component solutions of pure fatty acids and triglycerides, as well as a sesame oil sample to simulate a complex biological oil, were used to optimize the methodologies. Key parameters that were investigated included: HCl-to-oil ratio, temperature and reaction time. Pure free fatty acids were found to esterify under reasonably mild conditions (10 min at 50°C with a 2.1:1 HCl to fatty acid ratio) with 97.6 ± 2.3% recovery as FAMEs, while triglycerides were largely unaffected under these reaction conditions. The optimized protocol demonstrated that it is possible to use esterification reactions to selectively determine the free acid content, total lipid content, and hence, glyceride content in biological oils. This protocol also allows gas chromatography analysis of FAMEs as a more ideal analyte than glyceride species in their native state.

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.