529 research outputs found
Bench-scale demonstration of CO2 capture with an electrochemically driven proton concentration process
No full textA thorough experimental investigation of a bench-scale apparatus of the proton concentration process with two symmetrical MnO2 electrodes is presented, with the aim of continuous desorption of CO2 from a K2CO3 solution. The electrodes were fabricated through cathodic deposition, and their chemical states, morphology, and microstructural architecture were characterized with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Successful formation of MnO2 film was confirmed by XPS analysis, and the SEM images showed a uniform distribution of the film across the carbon substrate surface and along the strand, with an average thickness of ∼500 nm, thus making proton ion diffusion possible. Continuous and efficient desorption of CO2 from a K2CO3 solution was obtained when electrodeposited MnO2 electrodes were used in a flow-based proton concentration process. The amount of CO2 desorbed per area of the electrode was 12-fold higher than that of a similar system. The electrochemical nature of the proton concentration process offers substantial practical advantages for the future, especially if electricity can be sustainably produced from renewable sources
Improved CO2 Capture Performance of Electrochemically Mediated Amine Regeneration Processes with Ionic Surfactant Additives
No full textFor the effective reduction of global CO2 emissions, it is essential to develop and deploy efficient and cost-effective technologies for CO2 capture, especially from large point sources. We recently developed an electrochemically mediated amine regeneration (EMAR) system to replace traditional thermal desorption for the capture of CO2 from post-combustion flue gases. Despite EMAR effectiveness on a laboratory scale, concerns regarding the high gas-to-liquid ratio in the electrochemical cell and long-term instability of the electrodes need to be addressed before further scale-up of the process to a pilot plant and beyond can be entertained. Accordingly, we investigated the effect of using sodium dodecyl sulfate (SDS) as an anionic surfactant and dodecyltrimethylammonium bromide (DTAB) as a cationic surfactant on the process operation. It was found that it is advantageous to use an anionic surfactant for a system such as EMAR that contains hydrophilic electrodes and a positively charged electrochemically active species. The overall cell resistance was notably reduced when SDS anionic surfactant was used. The precipitation of copper particles observed in the anode outlet when no surfactant was used was effectively avoided when SDS was added to the electrolyte, resulting in electrode stability. In addition, smaller gas bubbles were produced in the presence of the SDS surfactant, which resulted in less blockage of the electrode by the gas with a resultant lower cell potential under constant current conditions, driving more efficient CO2 desorption. This led to an ∼25% reduction in the electrochemical energy requirement, the lowest ever achieved experimentally for the EMAR process. Overall, the addition of a very low concentration of SDS resulted in the successful circumvention of the important problems faced by the EMAR system regarding further scale-up
A Review of Electrospun Carbon Fibers as Electrode Materials for Energy Storage
No full textThe applications of electrospun carbon fiber webs to the development of energy storages devices, including both supercapacitors and lithium ion batteries (LIB) , are reviewed. Following a brief discussion of the fabrication process and characterization methods for ultrafine electrospun carbon fibers, recent advances in their performance as supercapacitors and LIBs anode materials are summarized. Optimization of the overall electrochemical properties of these materials through choice of thermal treatment conditions, incorporation of additional active components (such as carbon nanotubes, metal oxides, and catalysts), and generation of novel fibrous structures (such as core-shell, multi-channel or porous fibers) is highlighted. Further challenges related to improving the conductivity, surface area, and mechanical properties of the carbon nanofiber webs, as well as the scale-up ability of the fabrication technique, are discussed.United States. Dept. of Energ
Aerosol filtration using electrospun cellulose acetate fibers
No full textAerosol filtration using electrospun cellulose acetate filters with different mean fiber diameters is reported, and the results are compared with those for two conventional filter media, a glass fiber filter and a cellulose acetate microfiber filter. The performance of these filters was studied using two aerosols, one solid (NaCl) and one liquid (diethyl hexyl sebacate), under conditions of relatively high face velocity (45 cm/s). The experimental observations are compared to theoretical predictions based on single fiber filtration efficiency. Our results indicate that the mechanisms for single fiber filtration efficiency provide reasonable predictions of the most penetrating particle size (MPPS), in the range of 40–270 nm, percentage penetration from 0.03 to 70 %, and fiber diameter in the range from 0.1 to 24 µm. Using an analysis based on blocking filtration laws, we conclude that filtration by cake formation dominated in the case of NaCl aerosols on electrospun filter media, whereas filters with larger fiber diameter showed a transition in mechanisms, from an initial regime characterized by pore blocking to a later regime characterized by cake formation. The liquid aerosol did not exhibit cake formation, even for the smallest fiber diameters, and also had much smaller influence on pressure drop than did the solid aerosol. The electrospun filters demonstrated slightly better quality factors compared to the commercial glass fiber filter, at a much lower thickness. In general, this study demonstrates control of the properties of electrospun cellulose acetate fibers for air filtration application.Philip Morris Internationa
Polyvinylferrocene for Noncovalent Dispersion and Redox-Controlled Precipitation of Carbon Nanotubes in Nonaqueous Media
No full textWe report noncovalent dispersion of carbon nanotubes (CNTs) in organic liquids with extremely high loading (~2 mg mL[superscript –1]) using polyvinylferrocene (PVF). In contrast to common dispersants, PVF does not contain any conjugated structures or ionic moieties. PVF is also shown to be effective in controlling nanotube dispersion and reprecipitation because it exhibits redox-switchable affinity for solvents, while maintaining stable physical attachment to CNTs during redox transformation. This switchability provides a novel approach to creating CNT-functionalized surfaces. The material systems described here offer new opportunities for applications of CNTs in nonaqueous media, such as nanotube–polymer composites and organic liquid-based optical limiters, and expand the means of tailoring nanotube dispersion behavior via external stimuli, with potential applications in switching devices. The PVF/CNT hybrid system with enhanced redox response of ferrocene may also find applications in high-performance biosensors and pseudocapacitors.United States. Dept. of Energ
Nanoemulsions: formation, properties and applications
No full textNanoemulsions are kinetically stable liquid-in-liquid dispersions with droplet sizes on the order of 100 nm. Their small size leads to useful properties such as high surface area per unit volume, robust stability, optically transparent appearance, and tunable rheology. Nanoemulsions are finding application in diverse areas such as drug delivery, food, cosmetics, pharmaceuticals, and material synthesis. Additionally, they serve as model systems to understand nanoscale colloidal dispersions. High and low energy methods are used to prepare nanoemulsions, including high pressure homogenization, ultrasonication, phase inversion temperature and emulsion inversion point, as well as recently developed approaches such as bubble bursting method. In this review article, we summarize the major methods to prepare nanoemulsions, theories to predict droplet size, physical conditions and chemical additives which affect droplet stability, and recent applications.Eni S.p.A
Electrospun Carbon Nanofiber Webs with Controlled Density of States for Sensor Applications
No full textElectrospun carbon nanofiber (CNF) webs with controlled density of states (DOS) are synthesized through varying the carbonization conditions to manipulate the concentration of nanosized graphite domains. These materials exhibit adjustable electrochemical activity and biosensitivity: both electron transfer kinetics for various redox systems and direct electron transfer efficiencies with enzymes increase with the DOS of the CNF webs.United States. Dept. of Energ
Carbon Dioxide Capture Using an Electrochemically Driven Proton Concentration Process
No full texthe development of sustainable CO2 capture technologies is critical to address issues associated with global warming. In this context, the concept of an electrochemically driven proton concentration process is developed for the capture of CO2 based on modulation of the proton concentration in an electrochemical cell by a proton intercalating MnO2 electrode. The pH sensitivity of CO2 hydration is leveraged such that CO2 is absorbed as bicarbonate and carbonate ions at high pH values and desorbed as gas at low pH values. The electrochemical work requirement for the proposed proton concentration process to desorb CO2 captured from a flue gas stream is estimated to be 33.2 kJe/mol CO2, suggesting that this process is competitive with other similar electrochemical-based approaches. The experimental results show that the generated current in a symmetrical electrochemical cell with fabricated electrodes is effectively translated into proton intercalation/deintercalation reactions through reversible cycles, resulting in modulated proton concentrations
An Electrochemically-mediated Gas Separation Process for Carbon Abatement
No full textThis work describes a promising alternative to conventional thermal processes for absorber/desorber processing of for removal of CO[subscript 2] from flue gas streams at fossil fuel fired power plants. Our electrochemically-mediated amine regeneration (EMAR) process offers the advantages of an electrical system coupled with the desirable high output purities typical of amine sorbents that are difficult to achieve with most electric systems such as pressure-swing sorption, membrane separation, and oxy-fuel combustion. Preliminary experimental results are presented that demonstrate the feasibility of using ethylenediamine as the CO[subscript 2] sorbent and copper electro-cycling to isothermally modulate the amine affinity for CO[subscript 2]. Cupric ions entirely deactivate ethylenediamine at a ratio of 2:1 diamine to copper. Open-circuit potential measurements at 50°C indicate the required energy to desorb CO[subscript 2] and regenerate the ethylenediamine is 18 kJ/mole CO[subscript 2] under open-circuit conditions. Kinetic over-potentials are sufficiently low to ensure acceptable energy losses. Lower energies can be achieved by increasing the temperature or by changing the amine.Siemens Corporation (CKI Research Fund)United States. Advanced Research Projects Agency-Energy (Research Grant DE-AR0000083
Biguanide-, imine-, and guanidine-based networks as catalysts for transesterification of vegetable oil
No full textPolycationic systems based on poly(hexamethylene biguanide) (PHMBG), branched polyethyleneimine (PEI) and poly(N-vinylguanidine) (PVG) have been evaluated as heterogeneous catalysts for the transesterification of sunflower oil by methanol. Insoluble networks are synthesized via cross-linking of PHMBG by either 4,4′-methylenebis(N,N-diglycidylaniline) or polyisocyanate prepolymer, PEI with sebacoyl chloride, and PVG with 1,4-butanediol diglycidyl ether. PHMBG and its cross-linked networks appeared to be remarkably efficient catalysts, enabling 80–100% triglyceride conversion within 0.5 h at 70 °C. PEI-based networks catalyzed triglyceride transesterification with rates 8- to 12-fold slower than their PHMBG-based counterparts. The PVG-based networks, which were devoid of hydrophobic moieties, appeared to be inefficient catalysts due to limited accessibility of the basic guanidine groups to reactants. The PHMBG networks were shown to be recyclable by a simple centrifugal filtration. After 15 cycles of recovery and reuse, only 10–15% decline in performance was observed.National Center for Research Resources (Puerto Rico) (Grant P20 RR016470)National Center for Research Resources (Puerto Rico) (Grant S06 GM-08216)National Center for Research Resources (Puerto Rico) (Grant GM-08102
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