Devinder Mahajan

High flux ethanol dehydration using nanofibrous membranes containing graphene oxide barrier layers

In this study, pristine multilayered graphene oxide (GO) was coated by established methods onto a thin-film nanofibrous composite (TFNC) mat to form a high flux membrane for ethanol dehydration. The thickness of the GO layer was controlled from 90 to 300 nm by taking advantage of the self-assembly behavior of GO sheets. The low transfer barrier of the TFNC mat provides a distinct advantage due to its large bulk porosity (80%) with fully interconnected pore structures. Ethanol dehydration experiments showed that a 93 nm thick GO membrane had a permeate flux of 2.2 (kg m−2 h−1) and a separation factor of 308 with a feed solution containing 80 wt% ethanol and 20% water at 70 °C, making the GO–TFNC system superior to commercial polymeric membranes. For example, the permeate flux of GO–TFNC is twice as high as that of the polyvinyl alcohol (PVA)-based commercial membrane. The morphology of the GO–TFNC membrane and the mechanism of water transport in the GO layer were also elucidated using SEM, TEM and grazing incidence wide-angle X-ray scattering (GIWAXS) techniques.

Direct observations of three dimensional growth of hydrates hosted in porous media

The visualization of time-resolved three-dimensional growth of tetrahydrofuran hydrates with glass spheres of uniform size as porous media using synchrotron x-ray computed microtomography is presented. The images of hydrate patches, formed from excess tetrahydrofuran in aqueous solution, show random nucleation and growth concomitant with grain movement but independent of container-wall effect. Away from grain surfaces, hydrate surface curvature was convex showing that liquid, not hydrate, was the wetting phase, similar to ice growth in porous media. The extension of the observed behavior to methane hydrates could have implications in understanding their role in seafloor stability and climate change.

The role of nano-sized iron particles in slurry phase Fischer–Tropsch synthesis

Abstract The slurry phase Fischer–Tropsch (F–T) activity of three α-Fe2O3-based materials, two unsupported nano-sized, NANOCAT (3 nm) and BASF (20–80 nm), and a supported micron-sized (32.5 μm ) UCI, are compared with respect to total hydrocarbon production from synthesis gas (H2/CO∼2/1) at 513 K. Low temperature Mossbauer spectra of the quenched slurry samples after 120 h on-line show that all three catalysts are essentially a mixture of oxide and carbide phases with magnetite (Fe3O4) being the dominant phase. TEM images of the quenched samples reveal unexpected particle characteristics. While both unsupported nano-sized materials essentially avoid expected agglomeration, the micron-sized UCI transforms into nano-sized material. These results suggest a crucial role of nano Fe during F–T synthesis.

Imaging methane hydrates growth dynamics in porous media using synchrotron X-ray computed microtomography

Commercial-scale methane (CH4) extraction from natural hydrate deposits remains a challenge due to, among other factors, a poor understanding of hydrate-host sediment interactions under low-temperature and high-pressure conditions that are conducive to their existence. We report the use of synchrotron X-ray computed microtomography (CMT) to image, for the first time, time-resolved pore-scale methane CH4 hydrate growth from an aqueous solution containing 5 wt % barium chloride (BaCl2) and pressurized CH4 hosted in glass beads, all contained in an aluminum cell with an effective volume of 3.5 mL. Multiple two-dimensional (2-D) cross-sectional images show CH4 hydrates, with 7.5 µm resolution, distributed in patches throughout the system without dependence on distance from the cell walls. The time-resolved three-dimensional (3-D) images, constructed from the 2-D slices, exhibited pore-filling hydrate formation from dissolved CH4 gas, similar to natural CH4 hydrates (sI) in the marine environment. Furthermore, the 3-D images show that the aqueous phase was the wetting phase of the glass beads, i.e., the host and the formed hydrate were separated by an aqueous layer. These results provide some fundamental understanding of the nucleation phenomenon of gas hydrate formation at the pore scale. Pore-filling CH4 hydrate growth is likely to result in a reduced bulk modulus, and thus, could affect seafloor stability during the reverse phenomenon, i.e., dissociation of natural hydrate deposits.

Integrating low-temperature methanol synthesis and CO2 sequestration technologies: application to IGCC plants

Abstract Coupling a low-temperature once-through methanol synthesis process with CO 2 separation technology would provide an option for integrated gasification combined cycle (IGCC) power plants to address the CO 2 mitigation issue and also create the capability to utilize methanol as a peak-shaving fuel. Data are presented that show that several nickel complexes activated by alkoxide bases catalyze facile synthesis of methanol from synthesis gas (primarily a mixture of CO and H 2 ) in homogeneous liquid phase under mild conditions of temperature ( 2 mitigation. The potential of this low-temperature methanol synthesis approach is considered in light of the recent advances in CO 2 sequestration technologies. A successful development of this technology may also provide an atom-economical pathway to transport remote natural gas in the form of methanol, a liquid energy-carrier.

Characterizations of furfuryl alcohol oligomer/polymerization catalyzed by homogeneous and heterogeneous acid catalysts

AbstractThe liquid-phase oligomer/polymerization of furfuryl alcohol (FA) catalyzed by homogeneous and heterogeneous acid catalysts was investigated by Infrared (IR) spectroscopy. At room temperature and 100 °C, FA was not decomposed with metal oxide catalysts except for tungsten oxide, whereas amberlyst and sulfuric acid converted a furfuryl alcohol monomer into oligomer/polymer even at a room temperature. During FA oligomer/polymerization reaction, a strong C=O band observed in the IR spectra provided a diketone structure, which was not observed in the Raman spectroscopy. Based on the FA monomer color changings and IR spectra, tungsten oxide can be possibly applied as a heterogeneous catalyst for controlling the product distribution and avoiding a product separation issue from catalyst.

Biogas potential on Long Island, New York: A quantification study

Biogas is the product of anaerobic digestion of waste, whether occurring spontaneously in landfills or under controlled conditions in digesters. Biogas is viewed as an important energy source in current efforts to reduce the use of fossil fuels and dependency on imported resources. Several studies on the assessment of biogas potential have been made at regional, national, and global scales. However, because it is not economically feasible to transport biogas feedstock over long distances, it is more appropriate to consider local waste sources for their potential to produce biogas. An assessment of the biogas potential on Long Island, based on the review of local landfills, wastewater treatment plants, solid waste generation and management, and agricultural waste, found that 234 × 106 m3 of methane (CH4) from biogas might be harvestable, although substantial barriers for complete exploitation exist. This number is equivalent to 2.52 TW-h of electricity, approximately 12% of fossil fuel power generation on ...

Introduction to Special Topic: Energy Pathways to a Low-Carbon Society

Energy and carbon are at the nexus of climate change, environment, health, and socio-economic development. The imperative to move towards cleaner and renewable energy to reduce greenhouse gas is gaining significant public and private sector support. Reducing carbon in the atmosphere has fast emerged as a major means to achieve this, since carbon content can be measured and hence the pathways can be well-defined. The December 2009 Copenhagen Accord recognized “the scientific view that the increase in global temperature should be below 2 degrees Celsius on the basis of equity and in the context of sustainable development.” To achieve this goal, the emerging scenario (e.g., the International Energy Agency (IEA) Report: World Energy Outlook 2009) is that the atmospheric concentration of CO2 be stabilized at around 450 ppm. If global emissions peak in 2015, we estimate that annual reductions in CO2 concentration of up to 5% would be necessary, equivalent to the Kyoto Protocol targets. Delaying reductions beyon...

Occurrence State and Molecular Structure Analysis of Extracellular Proteins with Implications on the Dewaterability of Waste-Activated Sludge

The occurrence state and molecular structure of extracellular proteins were analyzed to reveal the influencing factors on the water-holding capacities of protein-like substances in waste-activated sludge (WAS). The gelation process of extracellular proteins verified that advanced oxidation processes (AOPs) for WAS dewaterability improvement eliminated the water affinity of extracellular proteins and prevented these macromolecules from forming stable colloidal aggregates. Isobaric tags for relative and absolute quantitation proteomics identified that most of the extracellular proteins were originally derived from the intracellular part and the proteins originally located in the extracellular part were mainly membrane-associated. The main mechanism of extracellular protein transformation during AOPs could be represented by the damage of the membrane or related external encapsulating structure and the release of intracellular substances. For the selected representative extracellular proteins, the strong correlation (R2 > 0.97, p < 0.03) between the surface hydrophilicity index and α-helix percentages in the secondary structure indicated that the water affinity relied more on the spatial distribution of hydrophilic functional groups rather than the content. Destructing the secondary structure represented by the α-helix and stretching the polypeptide aggregation in the water phase through disulfide bond removal might be the key to eliminating the inhibitory effects of extracellular proteins on the interstitial water removal from WAS.

Bipolar Plate Durability and Challenges

Durability and cost represent the two main challenges hindering the fuel technology from penetrating the energy market and competing with other energy systems. Since bipolar plates comprise more than 60% of the weight and account for 30% of the total cost of a fuel cell stack, extensive development in bipolar plate technology have been conducted by many researchers.