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11 INFLUENCE OF WATER ON SUPERCRITICAL FLUID EXTRACTION Tanya Smyth Pratte, Graduate Student Selma Guigard. Graduate Student Richard G. Zytner, Assistant Professor Warren H. Stiver, Assistant Professor School of Engineering, University of Guelph Guelph, Ontario, Canada, NIG 2W1 INTRODUCTION Supercritical Fluid Extraction (SFE) has many applications including separation of organics from water, coffee and tea decaffeination, food and seed oil extractions, solvent and monomer extractions from polymeric materials and regeneration of granular activated carbon.' Some potential advantages of SFE over conventional processes are reduction in energy requirements, high quality of extracted products that are free of solvents, cheap solvents and gentle treatment of natural products.2 Major areas of environmental research involving SFE include regeneration of adsorbents, oxidation of hazardous wastes, extraction of organics from aqueous streams and leaching of contaminated soil samples.3 In regard to the remediation of contaminated soils, the focus of much of the research has been on factors that control the rate of extraction and improvements on the extraction process on a small scale.3-4 One of the factors affecting SFE applications in site remediation is the water content of a contaminated soil. In addition to the natural water levels present at the site, the first step following excavation may be a soil washing operation for a volume reduction benefit. In a laboratory setting, drying of samples prior to extraction is viable; however, drying may be too expensive at contaminated site, where tons of soil are involved. Therefore, the effects of water on the extraction rate and on the final amount of contaminant extracted can be crucial in determining if SFE is a feasible option for soil remediation. Water could influence the extraction by changing the thermodynamics of the process or by changing the kinetics of the extraction. From a thermodynamic perspective, the water may affect both the affinity of the contaminant for the soil as well as changing the properties of the supercritical fluid. Water will preferentially sorb to mineral sites in the soil and can cause swelling and shrinking of the clay constituents in soil. As a result, the sorption of the contaminant is altered. Supercritical carbon dioxide phase will become more hydrophilic as water is dissolved into it. thus increasing the overall polarity of the solvent phase. From a kinetic perspective, water may act as a physical barrier between the supercritical phase and the contaminated soil surface. Extraction of a contaminant from the soil would require passing through this barrier, which could be limiting for low solubility constituents. The main objective of the research discussed in this chapter was the investigation of the impact water has on the supercritical fluid extraction of organics from soil. BACKGROUND Supercritical fluids are fluids that are above their critical temperature and pressure. At these conditions the gas and liquid phases of the fluid are indistinguishable. In the supercritical domain the fluid has a number of properties that are advantageous for its use as an extraction fluid. Supercritical fluids have low viscosities and high solute diffusivities, compared to ordinary liquids. Mass transfer is enhanced due to its high buoyant forces while the low surface tension allows 51 si Purdue Industrial Waste Conference Proceedings. 1996, Ann Arbor Press. Inc.. Chelsea. Michigan 48118. Printed in U.S.A. 95
Object Description
Purdue Identification Number | ETRIWC199611 |
Title | Influence of water on supercritical fluid extraction |
Author |
Pratte, Tanya Smyth Guigard, Selma Zytner, Richard G. Stiver, Warren H. |
Date of Original | 1996 |
Conference Title | Proceedings of the 51st Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,46351 |
Extent of Original | p. 95-104 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Date Digitized | 2009-10-27 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 95 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 11 INFLUENCE OF WATER ON SUPERCRITICAL FLUID EXTRACTION Tanya Smyth Pratte, Graduate Student Selma Guigard. Graduate Student Richard G. Zytner, Assistant Professor Warren H. Stiver, Assistant Professor School of Engineering, University of Guelph Guelph, Ontario, Canada, NIG 2W1 INTRODUCTION Supercritical Fluid Extraction (SFE) has many applications including separation of organics from water, coffee and tea decaffeination, food and seed oil extractions, solvent and monomer extractions from polymeric materials and regeneration of granular activated carbon.' Some potential advantages of SFE over conventional processes are reduction in energy requirements, high quality of extracted products that are free of solvents, cheap solvents and gentle treatment of natural products.2 Major areas of environmental research involving SFE include regeneration of adsorbents, oxidation of hazardous wastes, extraction of organics from aqueous streams and leaching of contaminated soil samples.3 In regard to the remediation of contaminated soils, the focus of much of the research has been on factors that control the rate of extraction and improvements on the extraction process on a small scale.3-4 One of the factors affecting SFE applications in site remediation is the water content of a contaminated soil. In addition to the natural water levels present at the site, the first step following excavation may be a soil washing operation for a volume reduction benefit. In a laboratory setting, drying of samples prior to extraction is viable; however, drying may be too expensive at contaminated site, where tons of soil are involved. Therefore, the effects of water on the extraction rate and on the final amount of contaminant extracted can be crucial in determining if SFE is a feasible option for soil remediation. Water could influence the extraction by changing the thermodynamics of the process or by changing the kinetics of the extraction. From a thermodynamic perspective, the water may affect both the affinity of the contaminant for the soil as well as changing the properties of the supercritical fluid. Water will preferentially sorb to mineral sites in the soil and can cause swelling and shrinking of the clay constituents in soil. As a result, the sorption of the contaminant is altered. Supercritical carbon dioxide phase will become more hydrophilic as water is dissolved into it. thus increasing the overall polarity of the solvent phase. From a kinetic perspective, water may act as a physical barrier between the supercritical phase and the contaminated soil surface. Extraction of a contaminant from the soil would require passing through this barrier, which could be limiting for low solubility constituents. The main objective of the research discussed in this chapter was the investigation of the impact water has on the supercritical fluid extraction of organics from soil. BACKGROUND Supercritical fluids are fluids that are above their critical temperature and pressure. At these conditions the gas and liquid phases of the fluid are indistinguishable. In the supercritical domain the fluid has a number of properties that are advantageous for its use as an extraction fluid. Supercritical fluids have low viscosities and high solute diffusivities, compared to ordinary liquids. Mass transfer is enhanced due to its high buoyant forces while the low surface tension allows 51 si Purdue Industrial Waste Conference Proceedings. 1996, Ann Arbor Press. Inc.. Chelsea. Michigan 48118. Printed in U.S.A. 95 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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