Supercritical extraction from aqueous solutions

Extraction from Aqueous Solutions Critical Fluid Technologies, Inc. has developed a continuous countercurrent extraction process based on a 0.5-oy 10-m column to extract residual organic solvents such as trichloroethylene, methylene chloride, benzene, and chloroform from industrial wastewater streams. Typical solvents include supercritical CO9 and near-critical propane. The economics of these processes are largely driven by the hydrophihcity of the product, which has a large influence on the distribution coefficient. For example, at 16°C, the partition coefficient between liquid CO9 and water is 0.4 for methanol, 1.8 for /i-butanol, and 31 for /i-heptanol. 

Supercritical carbon dioxide is widely used as an extracting agent, especially in the food industry. Contaminats are also extracted from aqueous solutions or solids by CO2 [3]. Aftac extraction, the hazardous compound is in C02 not in the water phase. Therefore, in an optimum incineration process, the compounds would be oxidized in the extracting agent CO2 as a second step of an integrated process [4,S]. 

Organic solvents at STP and under supercritical conditions are the most common extractants for soil organic matter. Supercritical C02 and, to a lesser extent, N20 have also been used to extract both native and organic contamination from soil. Humus is extracted using aqueous solutions, but otherwise, water is rarely used to extract organic compounds from soil. A list of common soil organic matter extractants is given in Table 12.2. 

Erkey, C. (2000), Supercritical Carbon Dioxide Extraction of Metals from Aqueous Solutions a Review, J. Supercrit. FI. 17, 259-287. 

Mochizuki, S., Wada, N., Smith, R. L., Inomata, H. (1999), Supercritical Fluid Extraction of Alkali Metal Ions using Crown Ethers with Perfluorocarboxylic Acids from Aqueous Solution, Anal. Commun. 36, 51. 

One important potential application of supercritical extraction is the recovery of polar organic compounds from aqueous solutions. Such mixtures arise frequently as products of biochemical syntheses. In many cases, the costs of the energy-intensive separations are high and there is substantial incentive for the development of more efficient processes. 

Supercritical fluids such as carbon dioxide can be used as solvents to extract organic compounds from aqueous solutions. In order to achieve recoveries of these products often in low concentration, cosolvents as methanol or other alcohols have been added to improve the solubility and the selectivity of the primary fluid. To optimize the extract recovery, the knowledge of phase equilibria of the ternary system carbon dioxide-methanol-water is required at different temperatures and pressures. 

Ever since the first supercritical fluid extraction of metals from aqueous solutions and silica using in situ chelation was reported [82], a number of approaches based on the use of various types of ligands to extract metals and, usually, subsequent ion-pairing, have been developed. The principal types of reagents used for this purpose are described below. 

Laitinen, A. and Kaunisto, J., Supercritical fluid extraction of 1-butanol from aqueous solutions,... 

Erkey, C., Supercritical carbon dioxide extraction of metals from aqueous solutions a review,... 

Due to the low solubility of disperse dyes in supercritical CO2, die addition of a co-solvent, such as ethanol is crucial to achieve extraction of disperse dyes from aqueous solution. Without sufficient edianol modifier, the supercritical CO2 extraction could not generate hi solvating power which lea to the high... 

The extraction of metals based on a membrane contactor system with conventional solvents is a process widely studied using different configurations, extractants, and extraction solvents. One of the upcoming applications of membrane contactors is supercritical extraction. This process is called porocritical extraction. Porocritical process or porocritical extraction is a commercial supercritical fluid extraction (SFE) technique that utilizes an hollow fiber membrane contactor (HFMC) to contact two phases for the purpose of separation. As an improvement, the extraction of Cu + from aqueous solutions by means of dense gas extraction was achieved by using a hollow fiber membrane contactor device [7]. The authors... 

H. Valdes, R. Sepulveda, J. Romero, F. Valenzuela, J. Sdnchez, Near critical and supercritical fluid extraction of Cu(II) from aqueous solutions using a hollow fiber contactor. Chemical Engineering and Processing 65 (2013) 58-67. 

Wang, J. S., Sheaff, C. N., Yoon, B., Addleman, R. S., Wai, C. M. (2009). Extraction of uranium from aqueous solutions by using ionic liquid and supercritical carbon dioxide in conjunction. Chemistry-A European Journal, 15, 4458-4463. 

J. Hedrick, The Extraction of Analytes from Aqueous Solutions Using Supercritical Fluids, Ph.D. Disertation, Virginia Tech, Blacksbnrg, VA, 1992. 

Table 4 Extraction of Sr + and Cs+ from Aqueous Solutions with Supercritical CO2 Containing a Crown Ether and a Fluorinated Counteranions...

CM Wai, YM Kulyako, BF Myasoedov. Supercritical carbon dioxide extraction of cesium from aqueous solutions in the presence of macrocyclic and fluorinated compounds. Mendeleev Commun 180-181, 1999. 

Supercritical Extraction. The use of a supercritical fluid such as carbon dioxide as extractant is growing in industrial importance, particularly in the food-related industries. The advantages of supercritical fluids (qv) as extractants include favorable solubiHty and transport properties, and the abiHty to complete an extraction rapidly at moderate temperature. Whereas most of the supercritical extraction processes are soHd—Hquid extractions, some Hquid—Hquid extractions are of commercial interest also. For example, the removal of ethanol from dilute aqueous solutions using Hquid carbon dioxide... 

In the extraction of biologically active compounds, care must be taken to avoid the loss of activity that often occurs by contact with organic diluents. Thus a series of systems have been developed specifically with these compounds in mind. The first of these uses mixtures of aqueous solutions containing polymers and inorganic salts that will separate into two phases that are predominately water. A second system uses supercritical conditions in which the original two-phase system is transformed into one phase under special temperature-pressure conditions. Also the active organic compound can be shielded from the organic diluent by encapsulation within the aqueous center of a micelle of surface active compounds. AU these systems are currently an active area for research as is discussed in Chapter 15. 

The feasibility of extracting substituted phenols from an aqueous solution with supercritical CO2 is reported A special extraction vessel was used in order to overcome the mechanical difficulty in retaining the liquid matrix in the extraction vessel. Solid phase trapping was utilized with a diol silica bonded phase. Methanol was used to rinse the trap. Below 300 atm extraction recovery paralleled CO2 pressure at fixed temperature. Phenol was least extractable while, 2,4-dichlorophenol yielded the greatest percent recovery. Above 300 atm extraction yield declined with pressure. It is theorized that at high CO2 density there is less mixing with the aqueous phase because of increased fluid-fluid interaction. 

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