Comparative removal of naphthalene by adsorption on different sand/bentonite mixtures

The purpose of this study was to advance the understanding of naphthalene (polycyclic aromatic hydrocarbon) adsorption on sand/bentonite mixtures in the context of their use in the lining of waste disposal facilities. Batch adsorption studies were carried out to estimate the adsorption capacities of sand/bentonite mixtures. Different percentages of the bentonite (0% to 12%) in sand/bentonite mixtures were tested. These mixtures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). It was found that the mixture with 2% of bentonite adsorbs the highest amount of naphthalene over the whole range of initial naphthalene concentrations studied (Co: 2.5-22 mg L-1); this optimal fraction was therefore selected. The effect of the initial naphthalene concentration, percentage of the bentonite in the sand/bentonite mixture and temperature on the adsorption was investigated. The adsorption isotherms, established for every percentage of bentonite, revealed that the naphthalene adsorption follows a linear Freundlich isotherm for the optimal fraction of bentonite (2%). The kinetic study showed that the process obeys a pseudo-second-order equation model. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) indicated an endothermic and spontaneous nature of the naphthalene adsorption. The adsorption of naphthalene is more favorable at high temperatures and activation energy (8.263 kJ mol-1) suggests a physical adsorption. Keywords: Adsorption; Naphthalene; Bentonite; Sand/bentonite mixture.

Ellipsometric Measurements of the Thermal Stability of Alternative Fuels

Thermal stability is an important characteristic of alternative fuels that must be evaluated before they can be used in aviation engines. Thermal stability refers to the degree to which a fuel breaks down when it is heated prior to combustion. This characteristic is of great importance to the effectiveness of the fuel as a coolant and to the engine's combustion performance. The thermal stability of Sasol iso-paraffinic kerosene (IPK), a synthetic alternative to Jet-A, with varying levels of naphthalene has been studied on aluminum and stainless steel substrates at 300–400 °C. This was conducted using a spectroscopic ellipsometer to measure the thickness of deposits left on the heated substrates. Ellipsometry is an optical technique that measures the changes in a light beam's polarization and intensity after it reflects from a thin film to determine the film's physical and optical properties. It was observed that, as would be expected, increasing the temperature minimally increased the deposit thickness for a constant concentration of naphthalene on both substrates. The repeatability of these measurements was verified using multiple trials at identical test conditions. Finally, the effect of increasing the naphthalene concentration at a constant temperature was found to also minimally increase the deposit thickness.

Process Simulation on Crude Naphthalene Purification by Extractive Distillation

The impurity of benzothiophthene can be removed by extractive distillation in the crude naphthalene purification process. A process simulation has been studied on the crude naphthalene purification. In the case of ensuring each fraction's naphthalene concentration, a sensitivity analysis is made to determine the optimal conditions by varying extractive distillation parameters such as the feed stage, the reflux ratio and the distillate rate. Besides controlling of the sensitive plate for the recovery section is also discussed.

Whole-Cell Biocatalysis for 1-Naphthol Production in Liquid-Liquid Biphasic Systems

ABSTRACT Whole-cell biocatalysis to oxidize naphthalene to 1-naphthol in liquid-liquid biphasic systems was performed. Escherichia coli expressing TOM-Green, a variant of toluene ortho-monooxygenase (TOM), was used for this oxidation. Three different solvents, dodecane, dioctyl phthalate, and lauryl acetate, were screened for biotransformations in biphasic media. Of the solvents tested, lauryl acetate gave the best results, producing 0.72 ± 0.03 g/liter 1-naphthol with a productivity of 0.46 ± 0.02 g/g (dry weight) cells after 48 h. The effects of the organic phase ratio and the naphthalene concentration in the organic phase were investigated. The highest 1-naphthol concentration (1.43 g/liter) and the highest 1-naphthol productivity (0.55 g/g [dry weight] cells) were achieved by optimization of the organic phase. The ability to recycle both free cells and cells immobilized in calcium alginate was tested. Both free and immobilized cells lost more than ∼60% of their activity after the first run, which could be attributed to product toxicity. On a constant-volume basis, an eightfold improvement in 1-naphthol production was achieved using biphasic media compared to biotransformation in aqueous media.

Occurrence of Naphthalene in Honey Consumed in Turkey as Determined by High-Pressure Liquid Chromatography

This study is the first report on an investigation of the naphthalene concentration in samples of contaminated honey consumed in Turkey. Naphthalene was detected using high-performance liquid chromatography with a diode array detector at 220 nm. In one suspected contaminated specimen, the presence of naphthalene was confirmed by gas chromatography with mass spectrometry (GC-MS) at a concentration of 1.13 μg/kg. The limit of detection was 0.023 μg/g and the limit of quantification was 0.078 μg/g with signal-to-noise ratios of 3 and 10, respectively. A total of 100 samples of commercially available honey obtained from markets (53 samples) and street bazaars (47 samples) were analyzed. Mean naphthalene recovery from honey known to be contaminated with 1 μg/g was 80.4% (SD = 4.84%, n = 7).

Measurement of Biologically Available Naphthalene in Gas and Aqueous Phases by Use of a Pseudomonas putida Biosensor

ABSTRACT Genetically constructed microbial biosensors for measuring organic pollutants are mostly applied in aqueous samples. Unfortunately, the detection limit of most biosensors is insufficient to detect pollutants at low but environmentally relevant concentrations. However, organic pollutants with low levels of water solubility often have significant gas-water partitioning coefficients, which in principle makes it possible to measure such compounds in the gas rather than the aqueous phase. Here we describe the first use of a microbial biosensor for measuring organic pollutants directly in the gas phase. For this purpose, we reconstructed a bioluminescent Pseudomonas putida naphthalene biosensor strain to carry the NAH7 plasmid and a chromosomally inserted gene fusion between the sal promoter and the luxAB genes. Specific calibration studies were performed with suspended and filter-immobilized biosensor cells, in aqueous solution and in the gas phase. Gas phase measurements with filter-immobilized biosensor cells in closed flasks, with a naphthalene-contaminated aqueous phase, showed that the biosensor cells can measure naphthalene effectively. The biosensor cells on the filter responded with increasing light output proportional to the naphthalene concentration added to the water phase, even though only a small proportion of the naphthalene was present in the gas phase. In fact, the biosensor cells could concentrate a larger proportion of naphthalene through the gas phase than in the aqueous suspension, probably due to faster transport of naphthalene to the cells in the gas phase. This led to a 10-fold lower detectable aqueous naphthalene concentration (50 nM instead of 0.5 μM). Thus, the use of bacterial biosensors for measuring organic pollutants in the gas phase is a valid method for increasing the sensitivity of these valuable biological devices.