Correlation between acoustic cavitation noise and yield enhancement of sonochemical reaction by particle addition

The mechanism of the effect of particle addition on sonochemical reaction is studied through the measurements of frequency spectrum of sound intensity for evaluating the cavitation noise and the absorbance for the liberation of iodine from an aqueous solution of KI as an index of oxidation reaction by ultrasonic irradiation in the presence or absence of alumina particles. As it is expected that both the acoustic noise and a rise in temperature in the liquid irradiated by intense ultrasound will increase with the number of collapsing bubbles, these are supposed to be the best tools for evaluating the relative number of bubbles. In the present investigation, it has been shown that the addition of particles with appropriate amount and size results in an increase in the absorbance when both the acoustic noise and the rise in the liquid temperature due to cavitation bubbles also increase. This suggests that the enhancement in the yield of sonochemical reaction by appropriate particle addition comes from an increase in the number of cavitation bubbles. The existence of particle in liquid provides a nucleation site for cavitation bubble due to its surface roughness, leading to the decrease in the cavitation threshold responsible for the increase in the number of bubbles when the liquid is irradiated by ultrasound. Thus, from the present investigation, it is clarified that the particle addition has a potential to enhance the yield in the sonochemical reaction.     

Pressure-induced reduction of shielding for improving sonochemical activity

The effect of hydrostatic pressure on chemical reactions induced by 20 kHz ultrasound has been studied using three different methods: the oxidation of potassium iodide, bubble cloud visualization studies, and sound attenuation measurements. The latter two have demonstrated that shielding of the ultrasonic wave is less pronounced at elevated pressures. Accordingly, the yield of iodine liberation increases with increasing pressure. At high static pressures, however, the less efficient cavitation dynamics dominate and the chemical reactivity decreases rapidly.     

Ultrasound-induced polymerization of methyl methacrylate in liquid carbon dioxide: a clean and safe route to produce polymers with controlled molecular weight

Ultrasound-induced cavitation is known to enhance chemical reactions as well as mass transfer at ambient pressures. Ultrasound is rarely studied at higher pressures, since a high static pressure hampers the growth of cavities. Recently, we have shown that pressurized carbon dioxide can be used as a medium for ultrasound-induced reactions, because the static pressure is counteracted by the higher vapor pressure, which enables cavitation. With the use of a dynamic bubble model, the possibility of cavitation and the resulting hot-spot formation upon bubble collapse have been predicted. These simulations show that the implosions of cavities in high-pressure fluids generate temperatures at which radicals can be formed. To validate this, radical formation and polymerization experiments have been performed in CO₂-expanded methyl methacrylate. The radical formation rate is approximately 1.5*10¹⁴ s⁻¹ in this system. Moreover, cavitation-induced polymerizations result in high-molecular weight polymers. This work emphasizes the application potential of sonochemistry for polymerization processes, as cavitation in CO₂-expanded monomers has shown to be a clean and safe route to produce polymers with a controlled molecular weight.     

Enhanced fluidity liquid chromatography for hydrophilic interaction separation of nucleosides

The application of enhanced fluidity liquid (EFL) mobile phases to improving isocratic chromatographic separation of nucleosides in hydrophilic interaction liquid chromatography (HILIC) mode is described. The EFL mobile phase was created by adding carbon dioxide to a methanol/buffer solution. Previous work has shown that EFL mobile phases typically increase the efficiency and the speed of the separation. Herein, an increase in resolution with the addition of carbon dioxide is also observed. This increase in resolution was achieved through increased selectivity and retention with minimal change in separation efficiency. The addition of CO₂ to the mobile phase effectively decreases its polarity, thereby promoting retention in HILIC. Conventional organic solvents of similar nonpolar nature cannot be used to achieve similar results because they are not miscible with methanol and water. The separation of nucleosides with methanol/aqueous buffer/CO₂ mobile phases was also compared to that using acetonitrile/buffer mobile phases. A marked decrease in the necessary separation time was noted for methanol/aqueous buffer/CO₂ mobile phases compared to acetonitrile/buffer mobile phases. There was also an unusual reversal in the elution order of uridine and adenosine when CO₂ was included in the mobile phase.     

柴油在超声波/Cu2+/H2O2中的氧化脱硫

为了实现生产低硫柴油和超低硫柴油的目标，以超声波为外加能源，构筑超声波/类Fenton试剂的柴油氧化脱硫反应体系，考察了水相pH值和超声功率这两个参数对柴油氧化脱硫效果的影响。实验结果表明，当类Fenton试剂的水相pH值为2.00左右时，其脱硫效果较好；无超声波下H2O2、类Fenton试剂、超声波/H2O2及超声波/类Fenton试剂的柴油氧化脱硫反应符合表观一级反应动力学规律。超声波功率的提高对氧化脱硫有明显的促进作用,这主要是由于功率的增加，有助于加速空穴的形成与内爆，从而促进反应的进行。     

Solubility measurements for the CH4 + CO2 + H2O system under hydrate–liquid–vapor equilibrium

Phase equilibria for the CH₄ + CO₂ + H₂O system have been investigated in the past, but mole fraction of methane and carbon dioxide in the bulk liquid phase has not been measured under hydrate–liquid–vapor equilibrium. Equilibrium liquid composition is very important as it defines the driving force for hydrate growth. This study presents the solubility of methane and carbon dioxide under H–Lw–V equilibrium. Emphasis is made on the effect of pressure along the respective isotherms on the equilibrium mole fraction of the individual hydrate formers in the liquid.     

Amine functionalised metal organic frameworks (MOFs) as adsorbents for carbon dioxide

Three different porous metal organic framework (MOF) materials have been prepared with and without uncoordinated amine functionalities inside the pores. The materials have been characterized and tested as adsorbents for carbon dioxide. At 298 K the materials adsorb significant amount of carbon dioxide, the amine functionalised adsorbents having the highest CO₂ adsorption capacities, the best adsorbing around 14 wt% CO₂ at 1.0 atm CO₂ pressure. At 25 atm CO₂ pressure, up to 60 wt% CO₂ can be adsorbed. At high pressures the CO₂ uptake is mostly dependent on the available surface area and pore volume of the material in question. For one of the iso-structural MOF pairs the introduction of amine functionality increases the differential adsorption enthalpy (from isosteric method) from 30 to around 50 kJ/mole at low CO₂ pressures, while the adsorption enthalpies reach the same level at increase pressures. The high pressure experimental results indicate that MOF based solid adsorbents can have a potential for use in pressure swing adsorption of carbon dioxide at elevated pressures.     

Production of succinic acid by anaerobiospirillum succiniciproducens

The effect of an external supply of carbon dioxide and pH on the production of succinic acid byAnaerobiospirillum succiniciproducens was studied. In a rich medium containing yeast extract and peptone, when the external carbon dioxide supply was provided by a 1.5M Na₂CO₃ solution that also was used to maintain the pH at 6.0, no additional carbon dioxide supply was needed. In fact, sparging CO₂ gas into the fermenter at 0.025 L/L-min or higher rates resulted in significant decreases in both production rate and yield of succinate. Under the same conditions, the production of the main by-product acetate was not affected by sparging CO₂ gas into the fermenter. The optimum pH (pH 6.0) for the production of succinic acid was found to be in agreement with results previously reported in the literature. Succinic acid production also was studied in an industrial-type inexpensive medium in which light steep water was the only source of organic nutrients. At pH 6.0 and with a CO₂ gas sparge rate of 0.08 L/L-min, succinate concentration reached a maximum of 32 g/L in 27 h with a yield of 0.99 g succinate/g glucose consumed.     

Dynamic adsorption properties of n-alkyl glucopyranosides determine their ability to inhibit cytolysis mediated by acoustic cavitation

Suspensions of human leukemia (HL-60) cells readily undergo cytolysis when exposed to ultrasound above the acoustic cavitation threshold. However, n-alkyl glucopyranosides (hexyl, heptyl, and octyl) completely inhibit ultrasound-induced (1057 kHz) cytolysis (Sostaric, et al. Free Radical Biol. Med. 2005, 39, 1539-1548). The efficacy of protection from ultrasound-induced cytolysis was determined by the n-alkyl chain length of the glucopyranosides, indicating that protection efficacy depended on adsorption of n-alkyl glucopyranosides to the gas/solution interface of cavitation bubbles and/or the lipid membrane of cells. The current study tests the hypothesis that "sonoprotection" (i.e., protection of cells from ultrasound-induced cytolysis) in vitro depends on the adsorption of glucopyranosides at the gas/solution interface of cavitation bubbles. To test this hypothesis, the effect of ultrasound frequency (from 42 kHz to 1 MHz) on the ability of a homologous series of n-alkyl glucopyranosides to protect cells from ultrasound-induced cytolysis was investigated. It is expected that ultrasound frequency will affect sonoprotection ability since the nature of the cavitation bubble field will change. This will affect the relative importance of the possible mechanisms for ultrasound-induced cytolysis. Additionally, ultrasound frequency will affect the lifetime and rate of change of the surface area of cavitation bubbles, hence the dynamically controlled adsorption of glucopyranosides to their surface. The data support the hypothesis that sonoprotection efficiency depends on the ability of glucopyranosides to adsorb at the gas/solution interface of cavitation bubbles.     

Suppression of sonochemiluminescence reduction at high acoustic amplitudes by the addition of particles

The effect of particle addition to a liquid or liquid surface on the sonochemiluminescence (SCL) was investigated using a luminol aqueous solution under ultrasonic treatment at 154 kHz. The acoustic-amplitude dependence of the SCL intensity was measured, in addition to capturing images of luminescent spatial patterns. At higher acoustic amplitudes, the cavitation efficiency dramatically reduces. This behavior is suppressed in the presence of particles. Particle addition provides nucleation sites for cavitation bubbles, lowering the cavitation threshold, and weakening the liquid surface vibration as the pressure amplitude decreases. It is shown that the reduction in SCL is suppressed under the addition of alumina particles into luminol aqueous solution. As the amount of alumina particles increases, the range of acoustic amplitude for suppressing the reduction in SCL is enlarged toward high amplitude, and the intensity of the SCL increases. Simultaneous addition of alumina particles into the solution and hydrophobic polytetrafluoroethylene (Teflon) particles onto the liquid surface is also effective. Examination of SCL images revealed that alumina particles added to the liquid at high acoustic amplitude caused the entire region of the reaction volume to be homogeneously luminous. If hydrophobic particles cover the solution surface, the surface vibration at high acoustic amplitude is fixed and the sound field becomes stable. This is responsible for suppression of the reduction in SCL and leads to a high rate of sonochemical reaction, even at high acoustic amplitude.     

Effect of ultrasound frequency on pulsed sonolytic degradation of octylbenzene sulfonic acid

It has been shown that pulsed ultrasound can influence the amount of surfactant that can adsorb to and decompose at the surface of cavitation bubbles. However, the effect of ultrasound frequency on this process has not been considered. The current study investigates the effect of ultrasound frequency on the pulsed sonolytic degradation of octyl benzenesulfonate (OBS). Furthermore, the effect of pulsing and ultrasound frequency on the rate of *OH radical formation was determined. OBS degradation rates were compared to the rates of *OH radical formation. In this way, conclusions were made regarding the relative importance of accumulation of OBS at cavitation bubble surfaces versus sonochemical activity to the sonochemical decomposition of OBS under different conditions of sonolysis. Comparisons of the data in this way indicate that sonolytic degradation of OBS depends on both the sonochemical activity (i.e., *OH yield) and the accumulation of OBS on cavitation bubble surfaces. However, under a certain set of pulsing and ultrasound frequency exposure conditions, enhanced accumulation of OBS at the gas/solution interface of cavitation bubbles is the sole mechanism of enhanced degradation due to pulsing. On the basis of this finding, conclusions on how pulsing at various ultrasound frequencies affects cavitation bubbles were made.     

Gas solubility of CO2 in aqueous solutions of N-methyldiethanolamine and diethanolamine with 2-amino-2-methyl-1-propanol

Gas solubility of carbon dioxide in an aqueous solution of 32.5 wt.% N-methyldiethanolamine and 12.5 wt.% diethanolamine with 4, 6, and 10 wt.% 2-amino-2-methyl-1-propanol has been measured, at 313.15, 343.15, and 393.15 K, over a range of pressure from 3 to 2000 kPa, using a chromatographic method for analysis of the liquid phase. The results of the gas solubility are given as the partial pressure of CO₂ against its mole ratio α (mol CO₂/mol alkanolamine) and its mole fraction at each temperature studied. The solubility of CO₂ in all the systems studied decreases with an increase in temperature and increases with an increase in the partial pressure of CO₂ at a given temperature and it is a function of the concentration of the mixture of alkanolamines in solution. The enthalpy of solution of CO₂ has been calculated from the experimental solubility data.     

High-pressure densities and P–T–x–y diagrams for carbon dioxide+linalool and carbon dioxide+limonene

Liquid and vapor densities for carbon dioxide+linalool, and carbon dioxide+limonene were measured by using a system consisting of two vibrating tube densimeters. The P–T–x–y diagrams and saturated liquid and vapor densities for these two binary mixtures were determined at 313, 323 and 333 K, respectively, as well as at pressures up to 11 MPa. The density of the saturated CO₂ phase increased with increasing pressure. At higher pressure, the density of the liquid phase decreased with increasing pressure, corresponding to an increasing amount of carbon dioxide.     

Strain induced nanocavitation and crystallization in natural rubber probed by real time small and wide angle X‐ray scattering

The concomitant appearance of crystallites and nanocavities under uniaxial strain is investigated by X‐ray scattering in a model natural rubber system. The nanocavities appear after crystallization and only when the true stress is above a critical cavitation stress σ_Cav. The presence of crystallites alone does not influence the calculation of the void volume fraction ?_void. The nanocavities formed are 20–50 nm in size with a constant aspect ratio. The presence of filler shifts the critical crystallization extension ratio λ_Cry, λ_Cav, and σ_Cav to lower values. The clear correlation between σ_Cav and the crystallinity at the onset of cavitation χ_C(λ_Cav) implies that the crystallites take most of the mechanical loading thus delaying the cavitation in the amorphous phase. Under cyclic loading, nanocavitation is significant only in the first loading and in the successive loadings if the extension ratio is above its maximum historical value. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1125–1138     

The Effect of Functional Groups on the Phase Behavior of Carbon Dioxide Binaries and Their Role in CCS

In recent years we have focused our efforts on investigating various binary mixtures containing carbon dioxide to find the best candidate for CO₂ capture and, therefore, for applications in the field of CCS and CCUS technologies. Continuing this project, the present study investigates the phase behavior of three binary systems containing carbon dioxide and different oxygenated compounds. Two thermodynamic models are examined for their ability to predict the phase behavior of these systems. The selected models are the well-known Peng–Robinson (PR) equation of state and the General Equation of State (GEOS), which is a generalization for all cubic equations of state with two, three, and four parameters, coupled with classical van der Waals mixing rules (two-parameter conventional mixing rule, 2PCMR). The carbon dioxide + ethyl acetate, carbon dioxide + 1,4-dioxane, and carbon dioxide + 1,2-dimethoxyethane binary systems were analyzed based on GEOS and PR equation of state models. The modeling approach is entirely predictive. Previously, it was proved that this approach was successful for members of the same homologous series. Unique sets of binary interaction parameters for each equation of state, determined for the carbon dioxide + 2-butanol binary model system, based on k₁₂–l₁₂ method, were used to examine the three systems. It was shown that the models predict that CO₂ solubility in the three substances increases globally in the order 1,4-dioxane, 1,2-dimethoxyethane, and ethyl acetate. CO₂ solubility in 1,2-dimethoxyethane, 1.4-dioxane, and ethyl acetate reduces with increasing temperature for the same pressure, and increases with lowering temperature for the same pressure, indicating a physical dissolving process of CO₂ in all three substances. However, CO₂ solubility for the carbon dioxide + ether systems (1,4-dioxane, 1,2-dimethoxyethane) is better at low temperatures and pressures, and decreases with increasing pressures, leading to higher critical points for the mixtures. By contrast, the solubility of ethyl acetate in carbon dioxide is less dependent on temperatures and pressures, and the mixture has lower pressures critical points. In other words, the ethers offer better solubilization at low pressures; however, the ester has better overall miscibility in terms of lower critical pressures. Among the binary systems investigated, the 1,2-dimethoxyethane is the best solvent for CO₂ absorption.     

Experimental study on equilibrium solubility (at low partial pressures), density, viscosity and corrosion rate of carbon dioxide in aqueous solutions of ascorbic acid

In this paper, ascorbic acid as a new carbon dioxide (CO₂) absorbent was investigated. The equilibrium solubility of CO₂ into 0.5, 1 and 1.5 mol dm⁻³ (M) aqueous ascorbic acid solutions were measured experimentally with a stirred batch reactor at total atmospheric pressure over the CO₂ partial pressure ranging from 0 to 45 kPa and temperatures between 298 and 313 K. The results of the gas solubility are presented as loading capacity (mol CO₂/mol ascorbic acid) as function of partial pressure of CO₂ for all experimental runs. Experimental results showed that solubility of CO₂ increases with increase in molar concentration of ascorbic acid solution at a given temperature and decreases with increase in temperature at a given concentration. The densities and viscosities of the ascorbic acid solutions were measured at the same conditions of the solubility measurement. Some corrosion rate tests were also performed on carbon steel at temperature of 308 K. It was observed that viscosity and corrosion rate increase when the molar concentration of ascorbic acid solution increases.     

Effects of temperature and anion species on CO2 permeability and CO2/N2 separation coefficient through ionic liquid membranes

The permeability of carbon dioxide (CO₂) through imidazolium-based ionic liquid membranes was measured by a sweep gas method. Six species of ionic liquids were studied in this work as follows: [emim][BF₄], [bmim][BF₄], [bmim][PF₆], [bmim][Tf₂N], [bmim][OTf], and [bmim][dca]. The ionic liquids were supported with a polyvinylidene fluoride porous membrane. The measurements were performed at T = (303.15 to 343.15) K. The partial pressure difference between feed and permeate sides was 0.121 MPa. The permeability of the CO₂ increases with temperature for the all ionic liquid species. Base on solution diffusion theory, it can be explained that the diffusion coefficient of CO₂ in an ionic liquid affects the temperature dependence more strongly than the solubility coefficient. The greatest permeability was obtained with the [bmim][Tf₂N] membrane. The membrane of [bmim][PF₆] presents the lowest permeability.The separation coefficient between CO₂ and N₂ through the ionic liquid membranes was also investigated at the volume fraction of CO₂ at feed side 0.10. The separation coefficient decreases with the increase of temperature for the all ionic liquid species. The membrane of [emim][BF₄] and [bmim][BF₄] gives the highest separation coefficient at constant temperature. The lowest separation coefficient was obtained from [bmim][Tf₂N] membrane which presents the highest permeability of CO₂.     

Severity function describing the hydrolysis of xylan using carbonic acid

Beech wood derived xylan to hydrolyzed to predominantly xylose monomer units after exposure to hot, compressed liquid water saturated with carbon dioxide. Similar treatment without CO₂ saturation resulted in only minor hydrolysis and a smaller fraction of monomers among the hydrolysis products. Severity of the hydrolysis reaction was correlated to reaction time, temperature, and carbon dioxide partial pressure and followed a function similar to those used to characterize mineral acid systems. Results from parallel hydrolysis experiments with an aqueous system and a very dilute sulfuric acid system allowed an approximation of the dissociation constant of carbonic acid in the temperature range of 170–230°C. Results suggest that carbonic acid may be a viable reagent for promoting hydrolysis without mineral acids, especially in the case of a bioprocessing plant that produces carbon dioxide.     

Correlation in spatial intensity distribution between volumetric bubble oscillations and sonochemiluminescence in a multibubble system

The correlation in spatial intensity distribution between volumetric oscillation of multibubble and sonochemiluminescence in an ultrasonic standing-wave field is investigated through the measurements of scattered light from bubbles by changing the measuring position in the direction of sound propagation and sonochemiluminescence with luminol. When a thin light sheet, finer than half the wavelength of sound, is introduced into the cavitation bubbles at the anti-node of the sound pressure, the scattered light intensity oscillates temporally. The peak-to-peak light intensity corresponds to the number of the bubbles which contribute to the sonochemical reaction because the radius for oscillating bubbles at pressure antinode is restrictive in a certain range due to the shape instability and the action of Bjerknes force that expels from anti-node bubbles larger than the resonant size. The experimental results show that at the side near the water surface, the peak-to-peak light intensity is larger in comparison with the intensity near the sound source, and this tendency becomes apparent at higher input power. These light scattering results correspond with the spatial intensity distribution of the sonochemiluminescence with luminol. Therefore, it is interpreted that most of the cavitation bubbles contributing to the sonochemical reactions in the standing wave field exist near liquid surface. Present method of light scattering in reference with the image of the sonochemiluminescence is promising for evaluating spatial distribution of violently oscillating cavitation bubbles effective for sonochemical reactions.     

Kinetic study of the nitric oxide oxidation between 288 and 323 K,under pressure,focus on the oxygen influence on the reaction rate constant

The sequestration of carbon dioxide fumes from oxyfuel combustion is used to reduce significantly the carbon dioxide emissions from coal-fired power plants. Impurities like nitric oxide, present in the fumes, can cause technical difficulties during the capture, the treatment, the transport, and the storage steps of the CO₂ fumes. The purpose of this study is to better understand the oxidation of nitric oxide under pressure in the presence of carbon dioxide and in the experimental condition of flue gas treatment. This reaction is known to be a third-order reaction, two order in nitric oxide and first order in oxygen. To examine the effect of the temperature, the pressure and the volume fraction of oxygen on the rate constant of oxidation, k₁, an autoclave is used. The first experiment studies the influence of the temperature between 288 and 323 K. The results found are in the form of an Arrhenius-type equation: k₁ = 810 exp^(620/T) and are in agreement with the literature. Carbon dioxide does not seem to have an influence on the rate constant, whereas our experimental measurements indicate an influence of the volume fraction of oxygen. The rate constant decreases when the oxygen volume fraction increases by up to 10%. Then the rate constant remains constant. This observation allows us to conclude that the mechanism involving the mechanism with a dimer of NO as an intermediate is more likely to be the mechanism involved in the nitric oxide oxidation in our experimental conditions: high pressure and ambient temperature. The rate constant k₂, k_–2, and k₃ were also estimated in these conditions.