41    EXTRACTION FRACTION AND EQUILIBRIUM
DISTRIBUTION COEFFICIENT OF
PHENOL AND p-CHLOROPHENOL IN
SUPERCRITICAL FLUID EXTRACTION
Chiehming J. Chang, Associate Professor of Chemical Engineering
Chin-Yang Chen, Professor of Environmental Engineering
College of Engineering
National Chung-Hsing University
Taichung, Taiwan 400
Hsi-Chang Lin, Graduate Research Assistant
Yuan-Ze Institute of Technology
#135, Yuan Tung Road
Taoyuan 320, Taiwan, R.O.C.
INTRODUCTION
Supercritical fluid extraction is based on the effective utilization of thermodynamic properties of
the solvent above its critical point.1-6 Since the density of a fluid near its critical point is sensitive to
small changes in pressure and temperature, the solvent power of a supercritical fluid can be related to
the liquid like density in the critical region. Supercritical fluid (SF) also exhibits gaslike transport
properties of high diffusivity and low viscosity. These properties allow the supercritical fluid extraction to achieve rapid extraction and phase separation.
Supercritical fluid extraction offers the advantage over both distillation and extraction. In consequence it can be applied to the recovery of heat-labile substances of low volatility and the solvent can
be perfectly separated by releasing the system pressure. A large number of applications of this
technology, have been proposed for the food, pharmaceuticals, chemical, coal and oil processing
industries.7""
Supercritical fluid extraction is capable of removing organics or toxins from soils and ground
waters.12-20 It is particularly useful in reducing the volume of wastes to be handled for further
treatment by combustion or biodegradation. In batch mode Van Leer and Paulaitis 2I measured the
solubilities of phenol and chlorinated phenols in supercritical C02. The purpose of this work is to
show the effectiveness of supercritical C02 in the decontamination of pollutants in a semi-continuous
flow system. As common pollutants in aqueous streams phenol and p-chlorophenol were chosen in
this study.
APPROACH
Apparatus and Procedure
The equipment layout is schematically shown in Figure 1. Liquid C02 (purity, 99.5%) was fed by a
duplex piston metering-pump (Milton Roy, NSI-33R) into the extractor equipped with three stainless
steel seamless tubes (30 cm in length, 1.2 cm in inside diameter). In order to have better mass transfer
between supercritical C02 and aqueous solution the extractor was packed up stainless steel wire-mesh
rings (200 mesh). The pressure was monitored by a digital pressure transducer (Druck, PDCR-910)
and controlled to within 0.05MPa. Temperatures in the extractor were measured by means of K-type
thermo-couples. The extractor was heated through three heating elements (Glas-Col, CC-10) controlled by a proportional and integral controller. A wet gas meter (Shinagawa, W-NK-1A) was utilized
to measure the flow rate and the total volume of C02 flowed through the extractor.
Carbon dioxide flow rate and the system pressure were controlled through a micro-metering valve
(Alltech, 2-way SSI valve) located between the micro-sampling valve and the wet gas meter.
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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