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SFE-CO 2 is a novel, promising, environmentally benign and inexpensive extracting method developed over the past few years to overcome environmental problems encountered due to the use of conventional solvents. One component (the extractant) is separated from another (the matrix) using SCF-CO 2 as the extracting solvents. This method is widely used for extracting heavy metals from environmental contaminant, bioactive compounds like antioxidants, plant medicine and natural products or remediating heavy metal contaminated soil by using good binding activity of SCF-CO 2 to heavy metal ions. The major advantages of the use of SCF-CO 2 as a solvent are its superior mass transfer properties, easy recycling and lack of secondary waste formation. We try to focus on the recent advances in SCF-CO 2 extraction technology for heavy metal extraction. In this review, the mechanism, procedure, and application of heavy metal extraction by SCF-CO 2 are summarized in a comprehensive manner and the factors affecting the extraction efficiency are analyzed. We try to provide some meaningful information about heavy metal extraction by SCF-CO 2 and make it a preferable option in heavy metal treatments.

A membrane gas absorption (MGA) process was evaluated in this work for CO2 capture from CO2/N2 gas-mixed streams at room temperature. The experimental study of a polypropylene (PP) hollow fiber membrane contactor in combination with the technique of CO2 absorption into aqueous solutions of activated methyldiethanolamine (MDEA) and MDEA as absorbents was carried out. A laboratory-scale setup, in which the solution with CO2 loading was able to be hot-regenerated into the solution without CO2 loading and used circularly, was established in this study. The effects of a variety of operation factors, such as gas and liquid flow rates, membrane pore-wetting, and liquid CO2 loading, on the separation performance of the membrane contactor were investigated. The absorption performances were compared between activated MDEA and MDEA. A mathematical model was developed to simulate the mass-transfer behavior of the membrane gas−liquid contactor. The experimental results show that the use of a membrane gas−liquid contactor with improved alkanolamines such as activated MDEA can be completely applied to CO2 capture. Low and steady liquid CO2 loading was able to be controlled by hot-regeneration. The CO2 absorption performance of activated MDEA was remarkably better than that of MDEA. The CO2 removal efficiency could reach more than 99% with activated MDEA. The average overall mass-transfer coefficient with activated MDEA was 2.25 times that with MDEA. The activator piperazine (PZ), even with a small quantity in the activated MDEA, plays a significant role in the improvement of mass transfer in MGA. A comparison of model estimations with experimental results indicates that estimations of the nonwetting mode are divaricated from experimental data. Taking partial-wetting of the membrane into account, the model simulation is validated with experimental data. Partial-wetting can result in significant membrane resistance to mass transfer in MGA.

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Densities and viscosities of aqueous solutions of potassium glycinate (PG) þ piperazine (PZ) composed of x PG /x PZ (mol/mol) = 1.0/0, 0.9/0.1, 0.8/0.2, 0.7/0.3, and 0.6/0.4 have been measured at (288.15, 303.15, 313.15, and 323.15) K. Surface tensions of aqueous solutions of (PG þ PZ) have been determined at 288.15 K. Correlations by means of mathematical fitting were developed for the predictions of density, viscosity, and surface tension of the aqueous solutions of (PG þ PZ) using the experimental data of this work. Results show that the densities and viscosities decrease as the temperature increases. The densities of the studied solutions decrease with the increase of PZ mole fraction in the solutions, while viscosities of the solutions increase. The surface tensions of the solutions almost decrease linearly as the PZ mole fraction in the solution increases from 0 to 0.4. The prediction values from correlation equations for density, viscosity, and surface tension are in good agreement with the experimental values. The correlation equations for each property can offer additional data for aqueous solutions of (PG þ PZ).

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