Use of inverse gas chromatography to account for the pervaporation performance in the microemulsion breakdown

Mass transfer phenomenon that occurs in the pervaporation process when applied to the microemulsion breakdown, was confirmed by the results of inverse gas chromatography. The stationary phase for this study was polydimethylsiloxane (PDMS), a hydrophobic polymer employed as a membrane in the pervaporation technique. The retention times of the different molecule probes (toluene, cyclohexane, and n-butanol) gave an insight into the extent of the interactions between each of these molecules and the stationary phase; these molecules were the components of the two microemulsions in study. The infinite dilution conditions allowed to determine the thermodynamic and the chromatographic parameters γ∞ (the infinite dilution activity coefficient), the Flory-Huggins parameter interactions χ∞12, and V0g (the specific retention volume), respectively. The magnitudes of the latter parameters threw some light on the permselectivity of the membrane in the pervaporation operation

Microemulsion breakdown by pervaporation technique: Effect of the alkyl chain length of n-alkanol, a cosurfactant of the microemulsion

Two sets of microemulsions, cyclohexane- and water-rich ones, were prepared with the following n-alkanols as cosurfactants: n-propanol, n-butanol, n-pentanol, and n-hexanol. The results showed the influence of the alkyl chain length of the n-alkanol on the permselectivity properties of the pervaporation technique in the breakdown of the microemulsions. The variations of the total flux rate J and the enrichment factor β were in parallel with the effect of the cosurfactant on the swelling extent of the PDMS membrane

Regeneration of transformer insulating fluids using membrane separation technology

Oxidation of oil/paper insulation initiates premature aging and introduces carboxylic acids with eventual increase in oil acidity, which hampers the properties of the oil. In this paper, a membrane separation technology-based purification process for aged insulation oil has been evaluated and reported. The intent of the present study is to eliminate carboxylic acids, dissolved decay contents and other colloidal contamination present in aged oil and enhance the useful life of oil. The potential of the membrane treatment process has been demonstrated using Ultraviolet Visible Infrared Spectroscopy and Fourier Transform Infrared Spectroscopy diagnostic measurements for oil and membrane. Additionally, membrane retention properties like membrane flux, retention coefficient, sorption time and membrane mass have been analyzed to understand the treatment process. To further evaluate the performance of the membrane and effectiveness of the treatment process, acidity, dielectric dissipation factor, relative permittivity, and resistivity measurements of the oil before and after filtration have been also reported. The proposed membrane purification method has been tested for Algerian utility in-service oil samples. It is inferred that, membrane filtration method is a simple and effective method for treatment of aged oils and aids in extending the remnant life of the oil. The procedure is economically attractive because of increasing prices for transformer liquids, cost effective and environmentally sounds

Influence of the hydrocarbon chain length of imidazolium-based ionic liquid on the dispersion and stabilization of double-walled carbon nanotubes in water

Imidazolium-based ionic liquids with a long hydrocarbon chain 1-methyl-1-ethanol-2-alkyl-imidazolium iodide ([M-E-Cn-Im] I, n = 13, 15 and 17) were used for the dispersion of DWCNTs in water.DWCNTs suspensions obtained were stable for more than a month, and no sedimentation was observed.The stability of the suspensions was investigated (measurement of optical density, zeta potential, parti-cle size, viscosity, and TEM images). Monitoring of the absorbance by UV/vis spectrophotometry for 20days showed that at low concentration (1 mM), the best suspension was obtained with the ionic liquid([M-E-C15-Im] I). At higher concentration (10 mM), the dispersion efficiency increased with the length ofthe hydrocarbon chain. This could be explained by the hydrophobic interaction between the hydrophobicmoieties of the ionic liquid and the CNTs. Therefore, we were able to stabilize DWCNTs using a low con-centration (1 mM) of imidazolium-based ionic liquids synthesized from natural compounds. This workhighlights the potential of imidazolium-based ionic liquids for the preparation of aqueous suspensionsof DWCNTs at high concentration with a limited amount of added surfactant (50 mg/L of DWCNTs with50 mg/L of ionic liquid)

Chemical functionalization of Xanthan gum for the dispersion of double-walled carbon nanotubes in water

International audienceAchieving stable suspensions of carbon nanotubes (CNTs) in water is still a challenge. Addition of surfactants is desirable as it allows keeping intact the intrinsic properties of the CNTs. However, for different applications, the potential toxicity of the surfactant is an important issue. Polysaccharides are among the best candidates and chemical modification can improve their intrinsic features. They can thus combine the properties of added synthetic counterparts with their intrinsic biocompatibility. In this work, we focused on the synthesis of hydrophobically modified Xanthan (Xan) with three derivatives (Diphenylmaleic anhydride, Phtalic anhydride, Epichlorhydrin-Phenol) to disperse CNTs. The dispersion and the stability against sedimentation of double walled carbon nanotubes (DWCNTs) have been investigated (rheological properties, zeta potential) as a function of pH and Xan concentration. Our results show that stable suspension of DWCNTs for 0.5% (w/w) could be obtained with the three derivatives of modified Xanthan gum in acidic and alkaline media while Xan itself is a very poor dispersing agent for CNTs, giving good evidence of the validity of our approach

Comparative study of the degradation rate of new and regenerated mineral oils following electrical stress

The objective of this contribution was to study the behaviour of new and regenerated insulating oil used in power transformers under the influence of an electric stress. To estimate the degradation rate of the dielectric fluids, one thousand (1000) successive breakdowns were generated according to the IEC 60156 standard. The parameters such as dissipation factor (Tan õ), resistivity, total acid number (TAN) and oil water Content were measured and examined following IEC/ISO standards. Good correlations have been obtained between TAN/resistivity and Tan õ which might provide a “picture” of the fluid condition. The dissolved oxidation products for the two dielectric fluids (after the application of electric breakdowns), was evaluated by infrared spectroscopy (FT-IR). The results obtained indicate that the degradation of the parameters is significant and confirms the influence of an alternative electric field (AC) on the new and regenerated oils. It was also suspected that inhibitors and antioxidants were removed from the oil after regeneration. Their concentration should therefore be monitored and replenished when necessary

In vivo antidiabetic effect and antioxidant potential of Stevia Rebaudiana mixed with Tragacanth gum in orange nectar

The objective of this research was to develop a novel low-sugar orange nectar using Stevia Rebaudiana and tragacanth gum, aiming to enhance the anti-hyperglycemic effect and antioxidant stability. The experimental design involved varying two levels of Stevia and tragacanth gum, including central points. The oxidative stability and organoleptic test were required for the selection. The impact of daily consumption of the optimal nectar on postprandial glycemia was assessed in diabetic Wistar rats.The results demonstrated that formulation F1, containing 0.5% tragacanth and 0.03% Stevia, achieved the highest organoleptic score (9.55) and exhibited the greatest stability, with half-life times of 83.87 days at 4 °C and 76.26 days at 25 °C. The in-vivo antidiabetic study revealed a positive effect of this formulation in preventing postprandial hyperglycemia and weight gain. This research clearly highlights the importance of incorporating 0.03% Stevia and 0.5% tragacanth in the formulation of low-sugar orange nectar to ensure functional efficacy and technological stability

Transformer oil reclamation by combining several strategies enhanced by the use of four adsorbents

From an environmental perspective, petroleum-based aged oils removed from power transformers are source of several pollutants and therefore cannot be disposed of without due care. The degradation of oil in in-service transformers is due to various factors concurrent with the operation of the units over several years. The present study proposes a new strategy to rejuvenate used mineral oils by combining centrifugation, dehydration and sorption with four different adsorbents: activated carbon (ACH), silica gel (SG), magnesium oxide (MO) and activated bentonite (AB). The process of regeneration proposed in this study resulted in a level of restoration that saw the used oil take on the characteristics of new oil (colour, dissipation factor, resistivity, permittivity, acid number). The results also showed that the optimum form of the re-refined base oil can be attributed to a 10% (w/w) quaternary mixture of the adsorbents, itself comprised of 1% ACH, 6% SG, 1% MO and 2% AB. The anticipated benefits are reduced risk of dielectric breakdown blamed for over 75% of extra high-voltage (EHV) power transformer failures and extended transformer life expectancy by retarding the solid insulation aging processes

Adsorption of Cadmium Ions from Water on Double-walled Carbon Nanotubes/Iron Oxide Composite

A new material (DWCNT/iron oxide) for heavy metals removal was developed by combining the adsorption features of double-walled carbon nanotubes with the magnetic properties of iron oxides. Batch experiments were applied in order to evaluate adsorption capacity of the DWCNT/iron oxide composite for cadmium ions. The influence of operating parameters such as pH value, amount of adsorbent, initial adsorbate concentration and agitation speed was studied. The adsorption capacity of the DWCNT/iron oxide adsorbent for Cd2+ ions was 20.8 mg g-1, which is at the state of the art. The obtained results revealed that DWCNT/iron oxide composite is a very promising adsorbent for removal of Cd2+ ions from water under natural conditions. The advantage of the magnetic composite is that it can be used as adsorbent for contaminants in water and can be subsequently controlled and removed from the medium by a simple magnetic process