Carbon Suspensions Research Articles

The effects of different nano materials on the strain and crack length sensing performance of smart concrete: Phenomenological models

Nineteen concrete mixtures with multi wall carbon nano tube (MWCNT), graphene, nano scale (waste of steel industry, iron oxide) and suspensions of nano sized iron, zinc, and a composite suspension of nano sized iron, silver, copper, zinc were designed with different volume percent. The electrical resistivity decreased 229%, 176%, 113%, 251% with additions of graphene, MWCNT, nano scale, composite suspension of nano-sized iron, silver, copper, zinc, respectively. The compressive strain sensitivity of the mixtures increased 244%, 211%, 311% with addition of graphene, MWCNT, nano zinc suspension, respectively. Tensile strain and crack length sensitivities of reference and graphene added mixtures which had the highest compressive strain sensitivity were determined. Strong linear relationships between compressive strain, tensile strain and crack length versus electrical resistance change were observed. Detailed phenomenological models were presented for relationship between the graphene amount, tensile strain and crack sensitivities.

Electrically conductive polymer composites based on elastic fiber

The possibility of obtaining electrically conductive composites by applying carbon suspensions to fibrous materials by aerosol spraying and screen printing, on printing equipment, which ensures high productivity, is shown. A manufacturing technology has been developed and the electromechanical properties of layered fibrous composites based on knitwear and graphite dispersion designed for the manufacture of strain and stress sensors used in "wearable electronics", robotics and medicine have been investigated. In an experimental study, it is shown that the conductive path, that is, the length of the chains of contacting filler particles decreases with tensile deformation due to the growth of microcracks in the material. The electrical resistance of growing microcracks has much higher values than the resistance of deformable piezoresistive material. Cracks can open and close in various ways during bending, torsion, stretching and compression deformation. The electrical conductivity of fibers and filaments significantly depends on the localization of electrically conductive particles on their surface or in volume. The location of the conductive chains on the surface or in the volume of the filaments determines the dependence of the electrical properties of composites on the state of the environment (composition, temperature, humidity). Preliminary studies of filaments with electrically conductive components of various chemical nature (metals, metal salts, carbon in various allotropic forms) show that changes in temperature and humidity significantly affect the resistivity of the conductive fiber. The paper presents data on the effect of temperature and humidity on the electromechanical properties of elastic fiber composites with graphite. When stretched to 15%, the calibration coefficient GF is reduced by 2 times at 100% humidity. The different influence of air temperature in the range of 100C-700C on the deformation and strain sensitivity during cyclic deformation up to 15% and 30% has been established. The presence of two ranges of deformation sensitivity is due to the difference in the mechanisms of elongation of knitwear due to straightening and stretching of threads. Different deformation and strain sensitivity of composites in the ranges of small and significant strains, at different temperatures and humidity of the air, has been established. The strain sensitivity reaches 130, and the strain sensitivity is 12 MPa -1, which is an order of magnitude higher than the stress sensitivity of known polymer composites with various electrically conductive fillers.

Significant electrolyte effect on Brønsted basicity of activated carbons

Brønsted basicity of solid particles is commonly evaluated by the pH of their aqueous suspensions, which is a simple and widely used analytical method. Herein, the pH of aqueous suspensions of activated carbons were measured to evaluate their Brønsted basicity. The results show that the pH of activated carbon suspensions varies greatly with residence time in a fast ascending and slowly descending pathway. Moreover, a significant electrolyte effect is found even in an ideal solution electrolyte of <0.01 M. Suspensions of basic porous carbon in 1 M NaCl or 0.5 M Na2SO4 solutions produce tenfold more OH− than those in ultrapure water, indicating much stronger Brønsted basicity. The great variation of pH with time and the significant electrolyte effect on pH can be attributed to the assembly of electric double-layers (EDLs) at the interface with the solid surface. Results on the isomerization of glucose into fructose demonstrate that basic activated carbons in electrolyte solutions have the potential to serve as a solid base. This work reveals a high degree of uncertainty in the pH of aqueous suspensions of carbons and provides new insight into the importance of EDLs at interfaces with solid surfaces with regard to Brønsted basicity of solids.

Separation and online optical characterization of fluorescent components of pyrogenic carbons for carbon dots identification

Optical features of fluorescent components of pyrogenic carbons as flame-formed carbon particulate matter (PM) were studied by setting up a facile and fast method (SEC-Abs/Fluo) based on size exclusion chromatography (SEC) coupled with UV–Visible absorption and fluorescence spectrometers as detectors. The SEC-Abs/Fluo method simultaneously allowed the molecular weight (MW) separation and identification of blue- and green-fluorescent PM components exhibiting size and spectroscopic features typical of carbon dots (CDs). The SEC-Abs/Fluo method allowed the online determination of quantum yield (QY) and optical band gap of fluorescent components also in strongly-scattering carbon suspensions so avoiding tedious pretreatment of carbon samples. From the detailed separation and analysis of blue- and green-fluorescent PM components along with two commercial pitches, aromatic species having MW > 1000 u and band gap <1–1.5 eV resulted to be scarcely or no fluorescent indicating these are the MW and band gap thresholds for fluorescence emission. Indeed, a sharp QY decrease was for the first time noticed in a narrower band gap (1–1.5 eV) range, where carriers can more easily tunnel to defects of the carbon network reducing fluorescence emission. The exponential increase of QY as the band gap rises was found with a more regular trend for the MW-segregated components in comparison to the bulk samples. The method can support and guide the choice of the optimal operating conditions to maximize CD formation and their purification from not-fluorescing components and can also be helpful in disentangling CD fluorescence attribution.

Flow Electrode Capacitive Deionization System with Simultaneous Desalting of Na+ and Gathering of Na+

Oceans contain many freshwater resources and metal elements that people need, so the rational development of marine resources can solve the two major problems of shortage of freshwater resources and metal elements for people. To solve these two challenges, a system was designed to obtain freshwater resources and metallic elements simultaneously. An ion enrichment module was added to the conventional flow capacitor deionization system to collect metal elements while the seawater was deionized. A flowing electrode allows the metal elements to enter the flowing electrode through the desalination ability. It transports the metal elements to the enrichment module through the fluidity of the fluid while reducing the ion concentration at the flowing electrode, thus reducing the effect caused by the rejection of the same ion and collecting and enriching the metal elements. We purchased activated carbon to test the feasibility of the system with different mass fractions of activated carbon suspensions. The results showed that the elemental enrichment capacity of the system increased from 12.291 to 14.795 mg, and the enrichment rate increased from 13.536 to 16.294 mg cm-2 h-1 as the mass fraction of activated carbon increased. Thus, the system accomplished the goals of desalination and metal collection simultaneously.

Predicting Fuel Cell Ink Aggregation

Polymer-electrolyte fuel cells (PEFCs) provide multisector decarbonization solutions including in transportation, manufacturing, and long-term energy storage. They have become increasingly popular in these areas due to their high efficiency, power density, and low (or zero) emissions compared to traditional fossil-fuel dependent processes. The PEFC catalyst layer is the most complex and key part of the cell, and is critical for optimizing PEFC performance. Several studies have explored the structure/function relationships of PEFC catalyst layers, yet the physics and interactions controlling its in-situ formation remain a mystery. PEFC catalyst layers are traditionally fabricated out of a catalyst supported on a carbon nanoparticle with an ionomer, traditionally perfluorosulfonic acids (PFSAs) such as Nafion, as a binder, which stabilizes the carbon suspensions in the ink dispersion. Recent studies demonstrated the importance of pH as an experimental parameter for both comparison and characterization of such systems.1 In this talk, we explore the interactions in the colloidal inks through detailed mathematical modeling. We propose a kinetics-based model representing species aggregation with pointwise interacting spheres that vary in charge through buried side chains for predicting the aggregation behavior of Nafion and carbon in solutions under varying conditions, such as solvent, Nafion wt% and carbon wt%. To demonstrate the accuracy and robustness of the model, we compare the results against a range of pH conditions and size distributions. The insights from the model help establish design criteria and guide future ink and process conditions.AcknowledgementsThis study was conducted under the Million Miles Fuel Cell Truck Consortium (M2FCT) funded by the Hydrogen and Fuel Cell Technologies Office in the Energy Efficiency and Renewable Energy Office of the U.S. Department of Energy under contract DE-AC02-05CH11231.References S. A. Berlinger, B. D. McCloskey, and A. Z. Weber, J. Phys. Chem. B, 122, 7790–7796 (2018).

Incorporation of Urea Fertilizer and Activated Carbon in Carboxymethyl Cellulose-Based Bioplastics

The high mobility of urea as a nitrogen nutrient in the soil leads to inefficient absorption by plants. Hence efforts to design a slow-release fertilizer (SRF) are significant. This paper reports the incorporation of urea fertilizer with carbon or zeolite in a bioplastic made of carboxymethyl cellulose as the matrix. The bioplastics were made by mixing the zeolite or activated carbon suspensions into a sodium carboxymethyl cellulose (Na-CMC) gel. Glycerol was then added as a plasticizer. Six variations of bioplastics were prepared, namely CMC-urea 0.5 and 1.0, CMC-urea-zeolite, CMC-urea-zeolite-glycerol, CMC-urea-activated carbon, and CMC-urea-activated carbon-glycerol. The weight ratio of CMC and urea fertilizer was kept constant at 2:1 since the resulted bioplastics showed higher texture transparency and homogeneity than those of bioplastics with a weight ratio of CMC to urea 1:1. The addition of zeolite increased the tensile strength of the bioplastics by about two times. While, the glycerol addition improved the elongation at break. The release of urea from the bioplastics was slower for bioplastics with zeolite than with activated carbon. The composite bioplastics may serve as a slow-release urea for agriculture.

ИССЛЕДОВАНИЕ ПРОЦЕССА ОЧИСТКИ ВОДЫ С ПРИМЕНЕНИЕМ ФЛОКУЛЯНТА «АММИАЧНЫЙ» НА ПРИМЕРЕ МОДЕЛЬНЫХ СИСТЕМ СТОЧНЫХ ВОД

The presented material shows the results of studies on the use of polyacrylamide flocculant «Ammonia» for flocculation treatment of model wastewater solutions. The role of the physico-chemical method of industrial wastewater treatment with the use of high-molecular flocculants is shown. The values of the effectiveness of the described research method are given. A brief description of flocculants is presented, the features of the use of components for various industries, such as chemical and petrochemical, are considered. The class of polyacrylamide flocculants of the AK-631 type used as an object of research is briefly characterized. In the course of the work, examples of various types of model systems (activated carbon, calcium carbonate, kaolin, quartz sand) are given. The parameters characterizing the flocculation process are described. The basic equations for calculating the characteristics of the process are given. In the course of the work, the particle sizes of the dispersed phase were determined, and the optimal concentration of polyelectrolyte was calculated. Graphical dependences confirming the experimental values of the quantities are considered. The influence of the nature and concentration of (poly)electrolyte on the flocculation rate of activated carbon suspensions of BAU and quartz sand is investigated. The values of turbidity, chromaticity and activity of the polyelectrolyte under consideration are calculated. Graphical dependences of the activity value on the volume of the injected reagent are given. Similar values were determined for polyacrylamide flocculants of the AK-631 type (A-930 and A-1510). The effect of the concentration of the substance introduced into the system on the activity of the component is described. The given values are presented in the form of graphical dependencies, a comparative analysis is carried out. The rates of clarification of suspensions in the presence of polyelectrolyte are investigated. Kinetic clarification curves of the suspensions under consideration are given. The values of the initial deposition rates of particles of dispersed phases for all considered polyacrylamide flocculants are calculated. The effect of the initial particle deposition rate on the flocculation activity of polyacrylamide flocculants with an increase in their concentration is described. The process of purification of the model system from zinc ions for the components under consideration is considered. Graphical dependences of the efficiency value on the volume of the injected substance are presented. A comparative analysis of the use of the component with polyacrylamide flocculants of the AK-631 type (A-930 and A-1510) was carried out.

Surface-Confined Destruction of Pollutants with H2O2 Assistance over Cu0@CuOx-N-Graphitic Carbon Suspensions

Surface-Confined Destruction of Pollutants with H₂O₂ Assistance over Cu⁰@CuO_<i>x</i>-N-Graphitic Carbon Suspensions

Dramatic Drop in Cell Resistance through Induced Dipoles and Bipolar Electrochemistry

The use of slurries of conducting particles has been considered a way to extend the electrode area in some energy storage electrochemical cells. When suspensions of conducting particles are used in electrolytes a decreased impedance is observed, even for concentrations much lower than the theoretical percolation limits. Indeed, it is known that polarization occurs when a conducting material is immersed in an electrolyte in presence of electric fields, and bipolar electrochemistry processes may occur. This work demonstrates the dramatic drop in resistance for electrochemical cells with just a few macroscopic conducting pieces immersed in the electrolyte, in the absence of any electrical contact, through bipolar induction. Furthermore, mediation of soluble redox species between adjacent induced poles of opposite charge results in an additional mechanism for charge transfer, contributing further to the decrease in impedance. Relevant parameters like size, geometry, and spatial occupation of inducible pieces within the electric field, are relevant. Remarkably, the effects observed can explain some empirical observations previously reported for carbon suspensions and slurries. Thus, no electronic percolation requiring particle contact, nor ordering, are needed to explain the good performance associated to lowered impedance These results suggest new engineering designs for electrochemical cells with enhanced currents.

High Performance Aqueous Li-Ion Flow Capacitor Realized Through Microstructure Design of Suspension Electrode.

Suspension electrode is the core of flowable electrochemical energy storage systems, which are considered suitable for large-scale energy storage. Nevertheless, obtaining suspension electrodes with both low viscosity and high conductivity is still a big challenge. In present work, spinel LiMn2O4 was chosen as an example to make suspension with low viscosity and high conductivity through microstructure morphology control of solid particles and the contact mode between active materials and conductive additives in suspension electrode. By coating a thin layer of polyaniline on the surface of spherical spinel LiMn2O4, the resulting suspension showed much higher electronic conductivity (about 10 times) and lower viscosity (about 4.5 times) as compared to irregular and bare spinel LiMn2O4-based suspension counterpart. As a result, the Li-ion flow capacitor based on LiMn2O4 and activated carbon suspensions exhibited a record energy density of 27.4 W h L−1 at a power density of 22.5 W L−1 under static condition to date, and can be smoothly work under an intermittent-flow mode. The strategy reported in this work is an effective way for obtaining suspension electrodes with low viscosity and high electronic conductivity simultaneously. It can not only be used in the flow capacitors, but also can be extended to other flowable electrochemical energy storage systems.

Comparative analysis of photothermal boiling of water enhanced by nano- and micro-particles of carbon black

The paper describes the effect of sodium dodecyl sulfate (SDS) on the steam generation during photothermal boiling of carbon nanofluids. The considered process finds promising applications for e.g. solar desalination where SDS may boost steam generation. Our study was carried out in a lab system boiling aqueous suspensions of carbon by means of artificial thermal radiation. The experiments demonstrate that the newly-produced nanofluids turn into suspension when no SDS is present in the fluid. The agglomeration of nanoparticles reduces the stability of the system yet degrades the steam generation by no more than 8.2%. The optimum particle concentration was about 2% wt. independently of whether SDS was present in samples. The steam was superheated by up to 12 K when using the surfactant which was 5–7 K higher than without SDS. The experimental data was supported by a theoretical analysis.

Light extinction and scattering from aggregates composed of submicron particles

The influence of the internal structure of inhomogeneous particles on their radiative properties is an open issue repeatedly questioned in many fields of science and technology. The importance of a refined description of the particle composition and structure, going beyond mean-field approximations, is generally recognized. Here, we focus on describing internal inhomogeneities from a statistical point of view. We introduce an analytical description based on the two-point density-density correlation function, or the corresponding static structure factor, to calculate the extinction cross sections. The model agrees with numerical predictions and is validated experimentally with colloidal aggregates in the 0.3–6 μm size range, which serve as an inhomogeneous model system that can be characterized enough to work without any free parameters. The model can be tightly compared to measurements with single particle extinction and scattering and spectrophotometry and suggests a simple behavior for 90° scattering from fractal aggregates as a function of extinction, which is also confirmed experimentally and numerically. We also discuss the case of absorbing particles and report the experimental results for water suspensions of black carbon for both the forward and 90° scattering properties. In this case, the total scattering and the extinction cross sections determine the single scattering albedo, which agrees with numerical simulations. The three parameters necessary to feed radiative transfer models, namely, extinction, asymmetry parameter, and single scattering albedo, can all be set by the analytical model, with explicit dependence on a few parameters. Results are applicable to radiative transfer problems in climate, paleoclimate, star and planetary formation, and nanoparticle optical characterization for science and industry, including the intercomparison of different optical methods such as those adopted by ISO standards.

Dissipative structures in thin films of cavitation-activated soot suspensions

This paper presents analysis of optical images of films obtained by evaporation (293 K) of a thin layer of low-concentrated (1% wt.) aqueous soot suspensions in a Petri dish. Suspensions of wood, fullerene and diamond-containing (after detonation synthesis) soot were prepared using hydrodynamic dispersion in a cavitation mixer with a wedge-shaped cavitator with the rotor’s angular velocity of rotation being 10000 rpm. The components of the hydrodynamic dispersion process are turbulent micro-mixing and bubble cavitation. As a result of intense turbulence, carbon suspensions assumed properties of non-equilibrium systems. The images of an optical microscope revealed self-organized dissipative micron-sized structures in the dried films being present there in the form of chain, branched and ring-shaped cluster fractals of various dimensions that look very similar to nanotubes. The self-assembling effect was identified for all the types of suspensions under study. The EPR method was used to study the change in the electronic structure of soot resulting from the exposure to high temperatures and pressures that occur when the cavitation bubbles collapse (cavitational activation). The dynamics of changes in dissipative structures in the process of film drying was monitored.

Effect of Carbon Support on Selectivity of CO2 Electrochemical Reduction to C2H4 on Copper Nanoparticles

The properties of supports influence the activities of carbon-supported Cu nanoparticle catalysts towards the CO2 electroreduction (CO2 RR) to hydrocarbon fuels and the reaction selectivity [1, 2]. Activity of Cu nanoparticles towards the CO2 electroreduction (CO2 RR) to hydrocarbon fuels and reaction selectivity is affected by carbon support [1, 2]. Recently, we compared electrocatalytic activities of Cu nanoparticles supported on reduced graphene oxide (RGO), single walled carbon nanotubes (SWNT) and onion-like carbon (OLC) towards CO2 reduction to CH4 and C2H4[3]. These nanostructured carbon supports share some common features, such as chemical and thermal stabilities and high specific surface areas. However, geometrical configurations for the three supports are completely different. While RGO can be represented by large, flat two-dimensional (2D) sheets, SWNTs are one-dimensional (1D) cylinders with an extremely high length-to-diameter ratio, and OLC consists of multiple zero-dimensional (0D) concentric stacked graphitic spheres. Among the three supported catalysts, Cu/OLC was found to be superior to the other two in terms of stability, activity and selectivity towards C2H4 generation. Herein, we examine the mechanism of the effect of nanostructured support on catalysts’ activity and selectivity. In addition, we determine whether supported Cu nanoparticles are durable enough to withstand potential excursions to open circuit potential (OCP), which are commonly encountered during CO2 electrolysis. Cu nanoparticles of 15-25 nm diameters on different carbon supports were synthesized by the reduction of CuCl2 using NaBH4 in suspensions of carbon supports in aqueous ethylene glycol solutions (20% v/v). X-Ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-Ray photoelectron spectroscopy (XPS) were used for ex-situ analysis of the supported nanoparticles. The catalytic activities of supported Cu nanoparticles and their selectivities towards hydrocarbon generation were evaluated using (1) a sealed rotating disk electrode (RDE) setup connected to a gas chromatograph (GC) and (2) a scanning flow cell (SFC) coupled to differential electrochemical mass-spectrometer (DEMS) [4]. Durability of supported Cu nanoparticles was evaluated using SFC connected to inductively coupled plasma mass spectrometer (ICP-MS) setup [5]. Fig. 1 a-d displays Faradaic efficiencies (FEs) as a function of applied potential for the three catalysts and Cu nanoparticles supported on vulcan carbon (VC) used as a reference. At -1.8 V, the FE of Cu/OLC catalyst towards C2H­4 production (Fig. 1 c) reaches 60%, which is one of the highest FEs reported to date. We propose that enhanced selectivity of the Cu/OLC catalyst towards the C2H4 production is due to the ability of the OLC support to reduce CO2 to CO more efficiently than the other two supports. The larger quantity of CO molecules generated on surfaces of OLCs dimerize on Cu NP (100) planes, and, subsequently, yield additional C2H4 molecules. An important metrics of an electrocatalyst catalyst is its stability under exposure to OCP. Fig. 2 demonstrates Cu susceptibility to dissolution under constant potential hold and its excursion to anodic potentials within the OCP range. At a reductive potential of -0.6 V, insignificant Cu dissolution is observed for the four catalysts triggered by reduction of Cu oxides. When potential becomes more positive, but not greater than 0.45 V, Cu is stabilized. At ~ 0.45 V, Cu dissolution current increases abruptly, demonstrating Cu anodic dissolution. Dissolution is similar for all four catalysts, which may be due to a local saturation by the products of dissolution. This implies that exposure of Cu-based cathodes of CO2 electrolyzers to OCP will lead to Cu dissolution.

CO2 Electrochemical Reduction to Hydrocarbon Fuels on Copper Nanoparticles Supported on Nanostructured Carbons

Recently [1,2], we reported activity and selectivity of Cu nanoparticles for electroreduction of CO2 to hydrocarbon fuels (CH4 and C2H4) on three nanostructured supports: reduced graphene oxide (rGO), single walled carbon nanotubes (SWNT) and onion-like carbon (OLC) [3]. Cu/OLC catalyst was found to be superior to the other two catalysts in terms of stability, activity and selectivity towards C2H4generation. We propose that the unusual Cu/OLC catalyst design offers superior activity and stability. The nanostructured catalyst envelops a shell of OLC around Cu nanoparticles; this layering acts as a filter that protects the catalyst surface from undesirable adsorbed species. Herein, we examine the effect of nanostructured support on catalysts’ activity and selectivity in more detail. In addition, we determine whether supported Cu nanoparticles are durable enough to withstand potential excursions to open circuit potential, which are commonly encountered during CO2electrolysis. Cu nanoparticles of 15-25 nm diameters on different carbon supports were synthesized by the reduction of CuCl2 by NaBH4. This procedure was carried out in suspensions of carbon supports in aqueous ethylene glycol solutions (20% v/v). X-Ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-Ray photoelectron spectroscopy (XPS) and pair-distribution function (PDF) were used for ex-situanalysis of nanoparticles. The catalytic activities of supported Cu nanoparticles and their selectivities towards hydrocarbon generation were evaluated using (1) a sealed rotating disk electrode (RDE) setup connected to a gas chromatograph (GC) and (2) a scanning flow cell (SFC) coupled to differential electrochemical mass-spectrometer (DEMS) [4]. Durability of supported Cu nanoparticles was evaluated using SFC connected to inductively coupled plasma mass spectrometer (ICP-MS) setup [5]. Fig. 1 shows partial currents of H2 (A), CH4 (B), C2H4 (C),CH3OH (D) and CO2electroreduction reaction total currents (E) measured on Cu/OLC, Cu/SWNT and Vulcan Carbon-supported Cu (Cu/VC) catalysts in DEMS-SFC configuration. Cu/VC catalyst is shown as a reference. Structural HRTEM and PDF (Fig. 2) analysis shows long-range ordering of the Cu-OLC catalyst and confirms high crystallinity of synthesized Cu nanoparticles. This presentation will provide analysis of the effect of support on catalytic activity, selectivity and durability of Cu nanoparticles as applied to electrochemical CO2reduction.

Flocculation with Lysozyme: A Non‐Enzymatic Application

Bioflocculants have been previously recognized as an alternative to synthetic polymers due to their renewable sources and biodegradability. In this study, the flocculating activity of lysozyme on kaolin suspensions was investigated and compared to a known flocculant, a cationic polyacrylamide. Lysozyme was found to significantly aid in the flocculation of kaolin particles. The flocculating activity of lysozyme on kaolin was affected by the pH of the suspensions, while the addition of Mg2+ and Ca2+ ions did not have a significant effect. Potential industrial applications such as the flocculation of powdered activated carbon and algae suspensions were investigated and the addition of lysozyme resulted in significant flocculation. Furthermore, the flocculating properties of lysozyme are independent of its enzymatic activity. Our results indicate that lysozyme acts as a low molecular mass cationic polymer, where the main mechanism for flocculation on negatively‐charged particles is charge neutralization. Other cationic proteins could potentially be used as bioflocculants to enhance solid‐liquid separation.

Kinetics of methane hydrate formation in the presence of activated carbon and nano-silica suspensions in pure water

New kinetic promoters must be researched for hydrate formation suitable for natural gas storage and transportation to push this technology towards economic feasibility. In this study, the kinetics of the methane hydrate formation have been investigated in the presence of activated carbon and nano-silica (0.5, 1.0 and 2.0 wt%) suspensions in an aqueous solution. Experiments were conducted at 8 MPa and 275.15 K using methane gas as the hydrate former. Particles (activated carbon and nano-silica) were analyzed using scanning electron microscope (SEM) and X-ray diffraction before use. Information on the number of moles of gas consumed during hydrate formation, induction time, rate of hydrate formation, water-to-hydrate and gas-to-hydrate conversion were investigated. It was seen that the kinetics of hydrate formation were more favorable at higher concentrations of particles of activated carbon and nano-silica in the suspension. The effect of the deactivation of activated carbon was also studied and has shown a reversed trend when compared to other particles, behaving as an inhibitor for methane hydrate formation. The rate of hydrate formation was enhanced in the presence of activated carbon and was on the higher side when compared to suspensions of nano-silica. The water-to-hydrate and gas-hydrate conversions observed were in-line with the trends seen in the moles of gas consumed, with activated carbon being more effective than the rest of the particles. The induction time was observed to be reduced in the presence of suspensions of activated carbon when compared to the other hydrate forming systems studied in this work. In general, the results show that both activated carbon and nano-silica have promoting effects on methane hydrate formation kinetics, however, the effect of activated carbon is significantly more pronounced. This study provides a precursor for an improved understanding on the role of particle suspensions for methane hydrate formation suitable for gas storage applications.

Continuous operation of an electrochemical flow capacitor

The electrochemical flow capacitor (EFC) has been recently introduced as a new concept for rapid and capacitive energy storage using flowable carbon-electrolyte suspensions. In our study, we investigate the EFC under static and constant flow conditions. Unlike in static carbon suspensions where poor particle-particle-contact and particle settling yield a highly resistive and time-dependent behavior, we show that flow operation of carbon suspensions reaches high Coulombic efficiency and stable energy density performance. Our results also indicate that the specific capacitance per total mass of carbon electrodes in flow operation is comparable to conventional bound carbon film electrodes.

Batch mode and continuous desalination of water using flowing carbon deionization (FCDI) technology

We report batch and continuous electrochemical desalination utilizing the ion adsorption capacity of a slurry containing carbon particles. Two carbon suspensions and the feed water are fed into the electrochemical cell operated according to the principle of membrane assisted capacitive deionization (MCDI). In a batch mode operation after the desalination step is complete the adsorbed ions are discharged from flowing electrodes to the same portion of water using polarity reversal. Operation with 15gNaCl/l water solution resulted in extremely high apparent salt adsorption capacity (SAC) value of 260mg/gdry carbon. This value is much higher than the highest value of SAC reported until now — 14.3mg/g. The reason for this phenomenon is not clear and further research is currently performed. In a new truly continuous process, both slurry streams are continuously recirculated between the desalination module and a regeneration/concentration module operated with the same functionality but with reversed potential. Ions desorb from the flowing electrodes and concentrate through the membranes into a purge stream. We prove continuous operation with desalination rate of more than 99% for an initial salt concentration of 1gNaCl/l. Concentration factors depend on the recovery, with 90% water recovery being demonstrated easily.