No abstract

Sonication at two frequencies (20 and 900 kHz) was carried out on dilute (220 ppm) aqueous solutions of chlorobenzene. The formation of chloride ions was followed using ion chromatography. The solutions became more colored with time; the absorbance maximum was around 270 nm. Some of the compounds remaining in the solution could be identified; they were chlorinated phenols, chloronaphthalene, mono and dichlorobiphenyls, etc. At the same acoustic power, the rate of chloride formation with 20 kHz ultrasound was greater when a probe with a larger tip area was used, but significantly less than the rate with 900 kHz. The use of ultrasound for conversion of chlorine in organic compounds in water to chloride can thus be performed more efficiently using a higher frequency and with a lower intensity (power per area). There is, however, a possibility that the toxicity of the aqueous solution is increased by such treatment.

Partitioning of pentachlorophenol (PCP) between water and CO 2 was investigated to determine the effects of pH and ionic strength on the value of the distribution coefficient, K. Decreasing the pH or increasing the ionic strength increased the value of K. The distribution coefficient was larger than that predicted by considering the extent of hydrolysis of the solute in the aqueous phase. However, impedance measurements suggest that negligible concentrations of ions exist in the CO 2 phase. Together, these two facts suggest that the aqueous phase hydrolysis equilibrium is shifted toward unhydrolyzed solute as PCP partitions to CO 2 . The value of K was smaller than the ratio of solubilities of the solute in the two phases, likely due to the effect of solute composition on the solute activity coefficients in each phase. Partitioning isotherms are also reported for the solutes pentachlorophenol, 2,3,4,5-tetrachlorophenol and 2,4dichlorophenoxyacetic acid at about 40 °C, between about 100 to 270 bar.

No abstract

Spectroscopic studies of the compound 2-nitroanisole in supercritical fluids CO2 and N2O show that π* values vary linearly with density. The solubility trends in these single component supercritical fluid solvents qualitatively followed the trends in solvent power predicted from π*. However, the relative solvent power predicted for CO2 and N2O based on π* resulted in an opposite order to what was determined experimentally through solubility measurements. The π* parameter may be of some use for solubility prediction if only a limited set of solute–solvent systems are considered. Measurements of π*, especially those in binary supercritical fluid solvents, suggest that π* could be a valuable tool for probing the solute-organized cybotactic region.

No abstract

Supercritical fluid technologies as alternative methodologies to conventional procedures are being explored for the direct extraction of acidic and polar contaminants from aqueous matrices. In support of the knowledge required to implement these novel methods, the partitioning of pentachlorophenol between water and liquid and supercritical CO2 has been characterized by determining distribution coefficients at (18.8, 41.7, and 59.8) °C from a saturated water solution (11.6 × 10-6 g/g solvent). The partitioning of pentachlorophenol from dilute solution (1.27 × 10-6 g/g solvent) was measured at (42.2 and 59.9) °C. Distribution coefficients were lower at this reduced concentration. Measurements were made at pressures up to about 280 bar. Comparison of the partitioning data to the solubility ratio of the solute in both phases contributes to the interpretation of relevant interactions in this complex system.

The adsorption of pentachlorophenol (PCP) from aqueous solutions using pristine multi-walled carbon nanotubes (MWCNTs) was studied kinetically and thermodynamically. The results showed that MWCNTs are good adsorbents for the elimination of PCP from aqueous solutions in a very short time compared with activated charcoal. The kinetics study showed that the adsorption of PCP is mainly due to the diffusion of PCP from the aqueous phase to the solid phase beside intra-particle diffusion. This intraparticle diffusion was more significant for activated charcoal compared with MWCNTs. The equilibrium adsorption of PCP at different temperatures was studied, and the adsorption isotherms were well described using different adsorption models. Thermodynamics study showed that the adsorption process was product-favored (enhanced) as the temperature decreased.