EPA/600/R-99/112
December 1999
SUPERCRITICAL EXTRACTION/LIQUID-PHASE
OXIDATION OF WASTES
by
Michael C. Mcnsinger
Amir Rehmar
Anil Goyal
Institute of Gas Technology
Des Plaines, Illinois 60018-1804
Cooperative Agreement CR822701
Project Co-Sponsors
Supcrfund Technology Demonstration Division
National Risk Management Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
IGT Sustaining Membership Program
1700 South Mount Prospect Road
Des Plaines, Illinois 60018-1804
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Page Intentionally Blank
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EXECUTIVE SUMMARY
This final report presents the work performed by the Institute of Gas Technology (IGT)
during the period from September 29. 1994 through May 31, 1998, under a Cooperative
Agreement (No. CR-822701-01-0) with the U.S. Environmental Protection Agency (EPA) for the
project "Supercritical Extraction/Liquid-Phase Oxidation of Wastes." The program was co-
sponsored by IGT's Sustaining Membership Program (IGT/SMP).
The overall objectives of this program were to develop and test IGT's Supercritical
Extraction/Liquid-Phase Oxidation (SELPhOx) process for hazardous wastes and contaminated
soils. Prior to the initiation of the experimental program, IGT prepared and submitted a Quality-
Assurance Project Plan (Task 1) to the EPA. The EPA subsequently approved the QAPP.
The experimental results and achievements made during the project are described below.
During the experimental program, IGT conducted a series of laboratory-scale
supercritical C02 extraction tests to evaluate the effects of C02 flow rate, temperature, and the
addition of a modifier on the extraction of polynuclear aromatic hydrocarbons (PAHs) from soil.
These tests were conducted in IGT's laboratory- and bench-scale supercritical extraction
equipment. The laboratory-scale tests were conducted with supercritical CO2 in once-through
mode. The bench-scale tests were conducted in CO, recirculation mode with activated carbon
adsorption of the PAHs. Overall, the results of these tests show that the extent of PAH extraction
from soil increases with temperature to a maximum at about 65°C. At temperatures above 65°C
the extent of PAPI extraction decreases.
In PAH adsorption tests with activated carbon; the results showed that lower, rather than
higher temperatures of the activated carbon increased the capture of PAHs from supercritical
CO2. A temperature of about 45°C yielded the highest recovery of PAHs. The results of tests
conducted with modilier (methanol) showed that a concentration of three percent yielded the
highest PAH extractions in the range of methanol concentrations, up to 10 percent in C07.
IGT also prepared the laboratory-scale batch WAO equipment for testing. Tests were
conducted with samples of contaminant-laden activated carbon slurry from the laboratory-scale
tests (Task 4).
IGT also designed and constructed a SELPhOx Field Test Unit (FTU) for testing with
samples of contaminated manufactured gas plant soil. IGT conducted shakedown tests in the
FTU. The FTU is skid-mounted and consists of a supercritical CO2 extraction vessel, an
activated carbon contaminant absorption vessel, a recirculating booster compressor, flow meters.
on-board computer data acquisition system, and a wet air oxidation vessel. The WAO vessel is
constructed with an agitator, means for sparging air through the system and means for
condensing water vapor back to the WAO reactor.
in
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The results of the supercritical CO, extraction shakedown tests showed that total
petroleum hydrocarbons (TPII) compounds were extracted from the soil. However the extent of
extraction was much lower than demonstrated in the laboratory-scale tests. Similarly, the
collection of the extracted TPIIs by the activated carbon was lower than expected.
These results demonstrate that the SELPhOx process requires additional development
work. Fluctuations in the flow meter readings were significant which caused uncertainty in the
accuracy of the flows. This must be confirmed. Also, the actual flow pattern of the supercritical
CO- flowing through the bed of contaminated soil must be determined. Supercritical CO-, may
have been flowing through the extraction cell at the prescribed flow rate; however, it may have
channeled through the contaminated soil in the bed with much of the contamination not
intimately contacting the CO:. A supercritical C02 flow distributor may be required in the
extractor as well as the activated carbon collector vessels. Both of these factors may have
contributed to the low extractions as well as the low carbon collection by the activated carbon.
1GT prepared a preliminary design and cost estimate for the SELPhOx Process. The
preliminary design and cost estimate was for a SELPhOx process plant with a capacity of about
300 tons per day (\2V-z ton/hour) of contaminated soil. The commercial plant consists of three
trains of extractors and one train of a wet air oxidizer. The total plant investment for this plant
was determined to be S16.300,000. Based on a 10-year equipment amortization and 6.0 percent
cost of capital, the yearly operating cost was estimated to be 59,333,000. This relates to a unit
processing cost ranging from Si 50 to S250 per ton.
IV
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TABLE OF CONTENTS
Page
EXECUTIVE SUMMARY iii
INTRODUCTION 1
ACHIEVEMENTS MADE DURING THE PROJECT 4
Quality Assurance Project Plan 4
Supercritical Extraction Tests 4
SELPhOx Field Test Unit 29
Field Test Unit and Data Analysis 31
Wet Air Oxidation Tests 32
Process Design and Economics 33
Project Management 33
CONCLT JSIONS AND RECOMMENDATIONS 34
ACKNOWLEDGMENTS 34
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LIST OF FIGURES
Figure
No.
1 IGT's Supercritical Extraction/Liquid-Phase Oxidation (SELPhOx) Process 2
2 Percentage Removal of PAHs From Soil 1 15
3 Number of Moles of PAHs Extracted From Soil 1 per Mole of CO, 16
4 Effect of Extraction Time on the Total Extraction Efficiency of PAHs
From Soil 1 at Different Flow Rates and Temperatures 17
5 Effect of Extraction Time on the Total Extraction Efficiency of PAHs
From Soil 2 (Extraction conditions - 4 mi/min, 45°C, 2000 psi) 19
6 Effect of Extraction Time on the Extraction Efficiency of PAHs From
Soil 2 (Extraction conditions - 2000 psi, 45°C, 4 ml/min) 20
7 Effect of Extraction Time on Total Percent Removal of PAFIs From
Soil 2 (Extraction conditions - 2000 psi, 45°C, 4 ml/min) 21
8 Effect of Concentration of Methanol on the Extraction of PAHs From
Soil 2 (Extraction conditions - 2000 psi, 45°C, 4 ml/min) 22
9 Effect of Temperature on Percentage Removal of PAHs From Soil 2
(Extraction conditions - 2000 psi, 4 ml/min. 5 wt % methanol in C02) 23
10 Removal Percentage of PAHs From Soil 3 in Recirculating Mode
(Extraction temperature in Test 20 and 21 are the same. Higher removal
percent in Test 21 is due to higher ratio of CO2 to soil) 27
11 Percentage of Extracted PAHs Adsorbed on the Activated Carbon
(At lower temperature, PAHs are adsorbed better on the activated carbon) 28
VI
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LIST OF TABLES
Table No.
1 Effect of Temperature, Flow Rate, and Extraction Time on the Extraction
of PAHs From Soil 1 7
2 Effect of Extraction Time on the Extraction Efficiency of PAHs
From Soil 2 9
3 Effect of Concentration of Mcthanol in Supercritical CO, on the
Extraction of PAHs From Soil 2 11
4 Effect of Temperature on the Extraction of PAHs From Soil 2
Using 5% Methanol in Supercritical C02 13
5 Results of Supercritical C02 Extraction Tests Conducted in CO,
Recirculation Mode 24
6 Extraction of Petroleum Hydrocarbons From Soil in CO,
Recirculation Mode 26
7 Summary of Conditions and Results of Shakedown Tests Conducted 31
in the SELPhOx FTU with Contaminated Soil
Vll
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Page Intentionally Blank
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INTRODUCTION
The overall objectives of this project, initiated September 29, 1994. were to develop and
test the Institute of Gas Technology's (IGT) Supercritical Extraction/Liquid-Phase Oxidation
(SELPhOx) process for hazardous wastes and contaminated soils. The data obtained during the
laboratory-scale tasks of the program were to be used in the design and construction of a
transportable SELPhOx Field Test Unit (FTU). The FTU was to be tested in Phase II to obtain
operational and performance data on the SELPhOx process. The results would then be used for
evaluating the process economics and for engineering design of commercial-scale unhs. The
SELPhOx process technology will be available for permanent cleanup of Superfund site soils.
soils from manufactured gas plant (MOP) sites, and other organic-contaminated soils.
The SELPhOx process, shown schematically in Figure 1, combines two proven
processing steps -
Supercritical Extraction (SCE) of organic contaminants with carbon dioxide (CO-:)
• Highly efficient and effective
• Uses environmentally acceptable C0:with or without modifiers as solubilizing agent
• Extraction leaves much of the original soil organic matter in place
• Produces no gaseous emissions
• Transportable unit can be developed
Wet Air Oxidation (WAO) destruction of the contaminants.
• Flamcless oxidation generates no fly ash, smoke, or oxides of sulfur or nitrogen
• Organic sulfur and chloride are converted to H,S04 and HC1 (or salts), which are present
and subsequently processed in the liquid phase
• Destruction levels exceeding 99 percent are routinely achieved
• Process is proven and thermally efficient
• Cost of treatment is low and less than other technologies, i.e., activated sludge treatment
• Heat generated by WAO can be utilized to increase thermal efficiency.
The two-stage SELPhOx process, linked by a separation step, offers great flexibility in
the removal and destruction of both high and low concentrations of organic contaminants. The
two distinct technologies are well suited for use in a single environmental remediation process.
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The primary goals of the two phases of the project were to:
Evaluate the effectiveness of the SELPhOx process on contaminated soils.
Determine the conditions of extraction that achieve the best economic efficiency.
Determine the best method and materials for separating extracted organics from CO2 and
conveying them to the WAO stage.
Determine the effectiveness of WAO to degrade contaminants extracted from the soil
Demonstrate operation of both SELPhOx process steps in a specially constructed
transportable Field test unit (FTU).
Perform an economic assessment of SELPhOx process.
CCNTAMiMATED
SOIL
CO, LOOP
SUPERCRITICAL
^EXTRACTION
IVESSfc-
i
CLEANED
SCIL
ACTIVATED
CARBON
CONTAMINANT
COLLECTION
VESSEL
HEAIESS
Figure 1. IGT's SUPERCRITICAL EXTRACTION/LIQUID-PHASE
OXIDATION (SELPhOx) PROCESS
An overview of planned activities for Phases I and II is presented below.
PHASE I
During Phase I, contaminated soil from a manufactured gas plant (MGP) site was to be
tested. IGT had a limited quantity of contaminated soil from an MGP site, which was used for
Phase I tests. These supercritical extraction tests were to be conducted on the soil samples using
CO2 recirculated around the extraction circuit (at pressure). Activated carbon was to be tested as
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a means for removing contaminants from the recirculating supercritical CO2 stream.
Contaminant-laden activated carbon was to be subjected to wet air oxidation (WAO) to
determine the extent of contaminant destruction and potential activated carbon recovery.
A preliminary design and economic evaluation was also to be made for a commercial-
scale SELPhOx process plant based on previously obtained laboratory-scale data. Also during
Phase I, the design and construction of the SELPhOx Field Test Unit (FTU) was to be
completed. Shakedown testing of the FTU was to follow in Phase II.
PHASE IT
In Phase II of the program, shakedown testing of the FTU was to be completed. Tests
were to be conducted in the FTU tests to evaluate the performance of the FTU with contaminated
soil depending upon availability of resources. The skid-mounted FTU could be transported to
Superfund or MGP sites for testing. FTU tests would determine the effects of temperature,
pressure, solvent-to-contaminant ratio, and modifier on extraction efficiency. The preliminary
design and economic evaluation performed in Phase I was also to be revised as necessary based
on the laboratory-scale and FTU test results.
The results from the SCE tests would be employed to reduce the cost of supercritical
extraction technology and would also extend the database for SCE. Results from the WAO step
would demonstrate destruction of hazardous compounds from SCE and provide data for
SELPhOx process design efforts. A key task of the project was to demonstrate the intermediate
separation step between the SCE and the WAO in which extracted contaminants were separated
from the supercritical CO2 via adsorption onto activated carbon.
The SELPhOx process can be used to extract and destroy the types of organic compounds
present at many Superfund and other contaminated sites. The SELPhOx process can be applied
to a wide range of organic pollutants including aliphatic and aromatic compounds, such as
gasoline, jet fuel, benzene, toluene, ethyl benzene, and xylene (BTEX). However, the process is
targeted toward sites contaminated by high concentrations of high-molecular weight 4- to 6-ring
PAHs, which are difficult to remove by other means.
The program is co-sponsored by the U.S. Environmental Protection Agency (EPA)
Superfund Innovative Technology Evaluation program under Cooperative Agreement No. CR-
822701-01-0 and IGT's Sustaining Membership Program. The EPA cooperative agreement was
approved on September 29, 1994. The 1GT/SMP program was initiated on November 28, 1994.
This final report describes the results of the work conducted by IGT from September 29,
1994 through May 31, 1998.
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ACHIEVEMENTS MADE DURING THE PROJECT
The achievements made during the project are summarized below for each of the six
experimental program tasks. The results are discussed in chronological order.
• Quality- Assurance Project Plan
• Supercritical Extraction Tests
• SELPhOx Field Test Unit
• Field Test Unit and Data Analysis
• Wet Air Oxidation Tests
• Process Design and Economics
Quality Assurance Project Plan
The objective of this task was to prepare the quality assurance project plan (QAPP). The
QAPP includes a detailed project description, quality assurance objectives, site selection and
sampling procedures, analytical procedures and calibration, data reduction, validation, and
reporting procedures, internal quality control checks, performance and systems audits,
calculation of data quality indicators, corrective action, and quality control reports to
management. The data quality indicators that were used to meet the quality assurance objectives
for the critical measurements included precision, accuracy, completeness, method detection limit,
representativeness, and comparability.
IGT's draft QAPP was submitted to EPA, which suggested comments and modifications.
1GT revised and resubmitted the QAPP. EPA subsequently approved the revised QAPP.
Supercritical Extraction Tests
The objectives of this task were 1) to determine the optimum conditions for removing
organic contaminants from selected soils, 2) to provide a baseline for comparison with tests to be
conducted in the FTU, and 3) to generate contaminant-laden activated carbon samples for testing
in the Wet Air Oxidation task. Other objectives included determining the effects of recycling
CO, through the extraction equipment on extraction efficiency and evaluating different types of
activated carbon to collect contaminants from the C02 in the separation stage.
For the tests planned in this task, an air-driven reciprocating piston pump was selected for
recirculating supercritical CO2 around the extraction circuit. A piston pump is compatible with
the high pressure of the system. While a piston pump is appropriate for the system from an
operational point of view, each stroke of the piston causes a pulse in the pressure of the system.
To dampen the pressure variation of the system, two pressure dampers (each 2 liters in volume)
were installed in the unit during the previous reporting period. Installation of those pressure
dampers reduced the pressure variations to less than about 100 psig per stroke. In addition to the
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pressure dampers, a back-pressure regulator (BPR) was installed downstream from the
rccirculating pump on its bypass. Installation of the BPR has reduced the pressure fluctuation of
the system to less than about 50 psig per stroke.
The flow rate of recirculating CO, in the system is measured using an orifice meter
system. M a given system pressure, the differential pressure across the orifice is proportional to
the flow of supercritical C(X In order to control the C02 flow rate around the SCE circuit.
actual measurements of the C02 flow rate through the orifice were needed at supercritical
conditions. The pressure of the C02 in the system was reduced in three steps from supercritical
conditions to atmospheric pressure before the C02 passed through the dry test meter for
measurement. The exit lines were equipped with electric heaters and a temperature controller to
avoid freezing and blocking of the lines by C0: as a result of Joule-Thomson cooling. Thus, for
a given differential pressure across the orifice, the flow rate of C02 flowing through the orifice
could be determined.
To study the effect of temperature on the amount of contaminants adsorbed by the
activated carbon, the line connecting the supercritical extractor and the activated carbon
adsorption bed was equipped with a heating tape and temperature controller. The length of the
process lines was reduced to minimize the quantity of materials that might be deposited in the
lines. The entire system was insulated.
Flow Calibration of Laboratory-Scale SCE Equipment
The objective of the laboratory-scale SCE equipment calibration was to obtain a
correlation for calculating the flow rate of supercritical CO, within the recirculation circuit. The
resultant correlation is a function of three parameters, namely the absolute pressure and
temperature at the orifice, and the pressure drop across the orifice. Since the flow rate of CO2
through the contaminated soil is a critical measurement, its accuracy is very important. A
number of tests were performed on the laboratory-scale SCE equipment to calculate the
parameters of the flow rate equation. In these tests, the flow rate was measured while holding
two of the variables (pressure, temperature, or pressure drop) constant and varying the other one.
The flow rate correlation is in the following form:
Q = k sqrt [ (P AP / T) ]
where 0 is the CO2 flow rate (SCF/h), k is the instrumentation coefficient, P is absolute pressure
(psia), AP is pressure drop (inches H2O), and T is absolute temperature. The coefficient k was
found to have the following relationship with absolute pressure of the CO,:
k = 5.25+ 0.0625 sqrt (P)
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Experiments. Results, and Data Analysis
A total of 25 tests were performed on two different soils each containing 572 and 1300
mg/kg of a suite of 16 PAH compounds, respectively. Eighteen of the SCE tests were conducted
in an analytical supercritical extraction unit (Hewlett-Packard, Model HP 780T SCF unit). The
other seven tests were conducted in IGTs SCE equipment modified for CO, recirculation and
contaminant adsorption on activated carbon. The objectives of these tests were to:
• Determine the effects of supercritical CO, flow rate, extraction time, temperature, and
concentration of modifier (methanol) in CO2 on PAH extraction.
• Evaluate different conditions of extraction and activated carbon adsorption on extracting
and capturing PAHs and total petroleum hydrocarbons (TPH) from soil with supercritical
CO, and supercritical C02/melhanol mixture.
Analyses were conducted to determine a suite of 16 PAHs in the feed soil, extracted soil,
and contaminant-laden activated carbon. In addition, total petroleum hydrocarbon (TPH)
analyses were conducted for some test samples to reduce laboratory expenses.
Analytical Laboratory Extraction Tests:
Tests 1 through 18 were conducted in the analytical laboratory SCE equipment with 1 to
2 gram samples each of contaminated soil. The extractions were dynamic with no static (or
holding) period employed. Tables 1 through 4 summarize the experimental conditions.
experimental results, and data analyses for these tests. Based on these results, the following
conclusions can be drawn.
The level of PAH extraction by supercritical C02 is affected by temperature. Higher
temperatures increase the percentage removal of PAHs (see Figure 2). The effect is more
pronounced for PAH numbers 1 through 6. For PAH numbers 8 through 16. increasing the
temperature from 45° to 145°C appears to decrease extraction slightly. Over the temperatures
tested (45° and 145°C), the number of moles of PAHs extracted per mole of C0; passing through
the soil increases with increasing temperature (Figure 3). This is clearly evident for PAH
numbers 1 through 8. The extraction of PAH numbers 9 through 16 does not appear to be
affected significantly by temperature. (Specific PAH compounds are numbered in the tables.)
The total efficiency of extraction declines with increasing extraction time (Figure 4). For
the same CO2 flow rate and temperature, the number of moles of PAHs extracted per mole of
CO-, declines as the extraction time increases. This behavior of the efficiency-time curve
suggests that PAHs in the soil exist in two different states: deposited and adsorbed. The rate of
removal of deposited PAHs is relatively fast and is controlled by local solid-supercritical fluid
equilibria. The rate of removal of adsorbed PAHs is relatively slow and is controlled by
adsorption-desorprion isotherms.
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Table 1. EFFECT OF TEMPERATURE, FLOW RATE. AND EXTRACTION
TIME ON THE EXTRACTION OF PAHS FROM SOIL 1
Experimental Condilions:
Row rate (ml/min)
P (psi)
T(°Q
Density (gm/ml)
Testtf ;
1
05
2
3
: 1-5 ] 4
4 ! 5
| 05
0.5
2000
45
6
4
7 ;
4 ,
i
1 145 !
0.72
Extraction time (min) j 50
Weight of dry sample (gin)
; 16.7
0.8773 j; 0.8459 '
6.25
0.9516
25
0.7783
100 i
0.7395 !
115
0.8925
0.25 ,
6.25 j
0.9934 '
experimental Results:
Compound fpAH#
Naphthalene
Acenaphthylene
Accnaphthene
Fluorence
Phcnanthrene
Anthracene
.Fluoranthene
Pyrcnc
Ber.zteOanthraccne
1
2
n
O
4
5
6
Soil 1
PAH (mg/kg soil) Removed From Soil 1
Test*
1
8.8 ! 8.8
j:
10.8 ': 1.7
3.1
11.4
35.1
9.7
7 1 91.9
t
8
9
Chrysene +• Triphcnyle... jj 10
Benzo(b)fluoranthene
BcnzoCklfluoranthcr.e
Banzo(a)pyrere
Indcno(l,2,3-cd)pyrene
Dibcn/.(a,h)anthracene
Renzo(
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Table 1 (continued). EFFECT OF TEMPERATURE, FLOW RATE, AND
EXTRACTION TIME ON THE EXTRACTION OF PAHS FROM SOIL 1
Data analysis:
PAH (mol/mol CO2) Removed From Soil 1
Comoound
PAH#
Naphthalene f 1
Acer.apr.thylene j 2
Acenaphthene | 3
E
Fluorence I, 4
Phcr.an:hrcnc f 5
Anthracene i 6
Fluoranthene
Pyrcr.c
Benz(a)anthracene
Chrysene + Tripher.ylene
Benzo(b)flv:oranthene
BcnzodOfluoranthcne
Benzo(a^pyrene
lndeno(l,2,3-cd)pyreno
Dibenz(a,h)anthracenc
Benzo(ghi)perylene
7
8
9
10
11
12
13
14
15
16
Total moles of PAH's/moie of CO2
1
1.47E-7
2.4DE-8
3.89E-8
2 I 3 i 4 ! 5
8.66E-8
2.44E-8
335E-8
1.46E-7 j 1.19E-7
4.08E-7
7.94E-8
2.S2E-7
2.90E-7
6.58E-8
6.29E-8
1.70E-3
2.04E-8
1.2SE-8
3.11 E-9
7.7IE-1C
1.55E-9
3.39E-7
556E-8
2.74E-7
3.14E-7
7.14E-8
6.87E-8
2.13E-8
2.37E-8
1.55E-8
3.74E-9
1.4SE-9
2.24E-9
1.05E-7
3.06E-8
3.77E-8
1.37F.-7
3.82E-7
6.92E-8
3.18E-7
3.59E-7
9.58E-8
9.37E-8
2.9SE-8
3.78E-8
25SE-8
7.58E-9
3.34E-9
5.05E-9
1.57E-6 |Tl.45E-6 || 1.74E-6
1.30E-7
325F.-8
4.69E-S
1.65E-7
4.08E-7
4.56E-3
1.48E-8
1.53E-8
5.71F.-8
1.S3E-7
6.83E-8 i| 3.45E-S
2.69E-7 1.73E-7
3.01E-7
5.83E-8
6.17E-8
151E-8
1.66E-8
1.C6E-8
138E-9
137E-9
1.38E-9 :
2.16E-7
5.74IZ-8
5.70E-8
1.S6E-8
2.04E-8
1.36E-8
3.93E-9
1.62E-9
2.29E-9
159E-^ | 9.19E-7
6 £ 7
652E-8
1.93K-8
255E-8
8.33E-8
2.49E-7
4.71 E-8
226E-7
2.66E-7
6.74E-8
650E-8
2.03E-S
223E-8
151 E-8
434E-9
4.39H-7
2.00E-7
1.31E-7
4.73F-7
1.24E-5
2.41E-7
3.09E-7
8.70E-7
1.38F-7
1.36E-7
2.83E-8
3.31E-3
1.S9E-S
2.16E-9
156E-9 | 114E-9
2.76E-9 f 2.16E-9
1.18E-6 j! 4.76E-6 |
PAH Percentage Removal From Soil 1
Tset#
Compound
'Naphthalene
Acenaphthylene
Acenaphthene
Fluorence
Phcnanthrene
Anthracene
Fluoranthene
Pyrcne
Benz(a)anthracene
jChrysene -r Triphcnylcne
Bcnzo(b)fliioranthene
Benzo(k)fluoranthene
Benzo(a)pyrcne
rndeno(l/2,3-cd)pyTene
Dibcnz(a,h)anthraccne
Benzo(ghi)perylene
PAH#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1
100.0
15.7
90.3
99.1
96.6
68.0
25.9
245
13.3
11.7
4.9
55
3.7
1.6
15 I 1.0 j
16 j 0.9
Total Removal, %
23.9
2
61.4
16.7
80.6
SA2
835
495
293
275
15.0
133
6.3
7.1
4.7
2.0 |
2.0
1.4
23.6
3
65.9
185
80.6
86.0
835
546
30.1
27.9
17.8
16.1
1&
10.0
6.9
3.6
4.1
2.7
25.2
4
50.0
12.0
61.3
632
54.4
33.0
ISA
14.3
6.6
65
2.4
2.7
1.7
0.4
1.0
0.5
13.6
5
73.9
23.1
87.1
911
103.7
70.1
42.8
43.3
275
252
117
14.0
9.4
4.8
5.1
32
34.8
6
875
25.0
116.1
111.4
116.0
79.4
45.7
44.1
26.7 ;
23.8
11.4
12.7
8.6
4.4
5.1
3.2 i
36.7 i
7
108.0
47.2
109.7
115.8
105.7
74.2
29.9
26.4
10.0
9.1
29
3.4
2.0
0.4
1.0
05 ;
25.7
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Table 2. EFFECT OF EXTRACTION TIME ON THE EXTRACTION
EFFICIENCY OF PAHS FROM SOIL 2
Experimental Conditions:
Flow rate (ml /min)
fernDGarture (°C)
Pressure (psi)
Density (g/rnl)
Extraction time (min)
Weight of dry sarr.ole (gm)
Tests
8
9
10
11
12
4
45
2000
0.72
6.25
0.5297
12.5
0.6733
25
0.709
30
0.6205
100
0.5662
Experimental Results:
Compound
Naphthalene
Acenaphthylene
Acenaphthene
Fluorene
Phenanthrene
Anthracene
!PAH if
1
2
3
4
5
6
Fl-joranthcne 3 7
Pyrcnc ' 8
Benz(a)anthracene
Chrysene - Triphenylene
Benzo(b)fluoranthenc
Benzo(k)fluoranthene
Benzo(a)pyrene
Indeno (1, 2,3 -cd)pyrene
Dibenz(a,h)anthracene
Bertzo(ghOperylcne
Total (mg/kg)
Q
10
11
12
13
14
15
16
PAH (mg/kg soil) Removed From Soil 2
Test*
Soil 2 j 8
23.4
51.6
95
45
26.9
26.2
242
318
127
128
54.6
72.5
113
39.8
14.4
45.1
12965
1.5
4
7.4
4.37
12.4
155
63.1
695
15.8
13
2.7
3.2
3.7
1.6
1.6
1.6
9
33
5.6
10.1
7.8
35.6
26.2
87.2
94.2
20.8
175
33
42
43
1.4
1.4
1.4
10
Z8
4.9
9.8
4.8
223
225
113
125
32.6
26.6
53
7.7
8.5
1.4
1.4
1.4
221.47 1 324.3 I 390
a , 1
11 [ 12
7.8
7.3
11.9
5.9
219
32,6
160
182
53.7
45.3
10
119
15
2
1.6
1.7
574.6
4.1
6.6
10.1
4.1
18.6
26.6
168
202
71.1
612
18
20.9
29.4
5.4
2.6
4.8
653.5
-------
Table 2 (continued).
EXTRACTION
Data Analysis:
EFFECT OF EXTRACTION TIME ON THE
EFFICIENCY OF PAHS FROM SOIL 2
Compound
Naphthalene
Acenaphlhylene
Acenaphthcr.e
Ruorene
Phcnanthrcne
Anthracene
FluoraiUhene
Pyrene
Benz(a)anthracene
Chrysene + Triphenylene
Benzo(b)fluorar.thcr.c
Bcnzo(k)fluoranthene
Benzo(a)pyrene
Indcno(l,2,3-cd)pyrcne
Dibenz(a,h) anthracene
Ben7o(ghi)pervlene
PAHS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Total mol PAHs/mol CO2 ;
PA1 1 (mol /mol CO2) Removed From Soil 2
Test*
8
1.5H-8
3.4E-8
6.2E-8
3.8E-8
9.0E-8
1.1E-7
4.0E-7
4.4E-7
9.0E-8
7.4E-3
1.4E-8
1.6E-8
1.9E-8
75E-9
7.5E-9
7.5E-9
1.4E-6
9
2.1 E-8
3.0E-8
5.4E-8
3.9E-8
1.6E-7
1.2E-7
3.5E-7
3.8E-7
7.5E-8
6.3E-8
1.1E-8
1.4E-8
1.4E-8
4.2E-9
4.1E-9
4.2E-9
10
9.4E-9
1.4E-8
n
1.2E-8
9.1 E-9
2.8E-8 ] 1.5E-8
1.3E-8 j 6.7E-9
5.4E-8 j| 2.7E-8
5.5E-8 j 3.5E-8
2.4E-7
2.7E-7
15E-7
1.7E-7
12
2.8E-9
3.8E-9
5.7E-9
2.1 E-9
9.0E-9
1.3E-8
7.2E-8
8.6E-8
i
6.2E-8 ] 45E-8 j 2.7E-8
5.1E-8 j 3.8E-S
9.1 E-9 75E-9
1.3E-8 ] 9.7E-9
1.5E-8
2.2E-9
2.2E-9
2.2E-9
1.4E-6 | 8.4E-7
1.1 E-8
1.4E-9
1.1E-9
1.2E-9
5.4E-7
2.3E-8
6.2E-9
7.2E-9
l.OE-8
1.7E-9
8.1E-10
15E-9
2.7E-7
Compound
Naphthalene
Accnaphthylcnc
Acenaphthene
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Benz(a ) an th ra cene
Cnrysene +• Triphenyle...
Benzofb) fl.uora n t hene
Benzo(k)fiuoranthene
Beazo(a)pyrene
Indenod^^-cdjpyrene
Dibenz(a,h)anthracene
Bcnzo(ghi)porylcne
PAHS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Total Removal, %
PAH Percentage Removal From Soil 2
Tests
8
6.41
7.75
77.89
108.22
46.10
59.16
26.07
21.86
12.44
10.16
495
4.41
3.27
4.02
11.11 !
3.55 :
17.08
9 ; 10
14.10
10.85
10632
173.33
132.34
100.00
36.03
29.62
16.38
13.67
6.04
5.79
3.81
352
9.72
3.10
25.01
11.97
9.50
103.16
106.67
82.90
85.88
46.69
39.31
25.67
20.78
9.71
10.62
752
352
9.72
3.10
11 I 12
33.33
14.15
125.26
131.11
92.57
124.43
66.12
57.23
42.28
35.39
18.32
17.79
13.27
5.03
11.11
3.77
30.08 || 44.32
1752
12.79
10632
91.11
69.14
10153
69.42
6352
55.98
47.81
32.97
28.83
26.02
1357
18.06
10.64
50.40
10
-------
Table 3. EFFECT OF CONCENTRATION OF METHANOL IN SUPERCRITICAL
CO, ON THE EXTRACTION OF PAHS FROM SOIL 2
Experiments Conditions:
Test*
11 13 14
15
Flow rate (ml/min) [ 4
Temperature (°C)
Pressure (psi)
Extraction time (min)
%me-OH in CO2
45
2000
50
0 j 3 5
10
Experimental Results:
PAH (mg/kg soil) Removed From Soil 2
Test#
Compound
Naphthalene
Acenaphthylene
Acenaphthene
Fluorence
Phr.nanihrene
Anthracene
Fluoranthene
Pyrcnc
Benz(a)anthracene
Chrysene + Triphenylene
Benzo(b)fh:oranthene
Beazo(k)fiuoranthene
Ben7o(a)pvrcne
Indeno(l,2,3-cd)pyrene
Dibenz(a,h)anthracene
Benzo(ghi)pervlene
PAH#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Soil
23.4
51.6
9.5
4.5
26.9
262
242
318
127
128
5-4.6
723
113
39.8
14.4
45.1
11
7.8
73
11.9
5.9
24.9
316
160
182
53.7
45.3
10
119
15
2
1.6
1.7
13
0.6
101
0.6
5.2
42.4
375
261
302
119
115
36.7
46
61.8
13.4
5.4
113
14
0.9
8.9
0.9
0.9
12.4
16.7
210
258
104
99.1
29.4
41.8
512
11.1
5.4
9.7
15
0.8
11.1
0.8
0.8
10.2
14.4
175
218
97
95.1
-10.4
45.1
72.7
20.1
!
8
19.2
11
-------
Table 3 (continued). EFFECT OF CONCENTRATION OF METHANOL IN
SUPERCRITICAL C02 ON THE EXTRACTION OF PAHS FROM SOIL 2
PAH'S Percentage Removal From Soil 2 Using 0, 3, 5, and 10% Methanol in Supercritical CO2
Compound
Naphthalene
Acenaphthylene
Acenaphthene
Fjuorence
Phenanthrenc
Anthracene
Fluoranthene
Pyrcne
Benz (a) anthracene
Chrysene + Triphenylene
Bcnzo(b)fluoranthene
Benzo(k)fiuoranthcnc
Bartzo(a)pyrene
lndeno(l,2,3-cd)pvrene
Dibcnz(a,h)anthraccnc
Bcnzo(ghi)perylene
Total PAH Removal, %
PAHS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Test*
11 [ 13
33.3
14.1
125.3
131.1
916
124.4
66.1
572
42.3
35.4
18.3
17.8
13.3
5.0
11.1
3.8
! 44.3
16
19.8
6.3
115.6
157.6
143.1
107.9
93.0
93.7
89.8
672
63.4
54.7
33.7
375
25.1
82.4
14
3.8
17.2
95
20.0
46.1
63.7
86.8
81.1
81 .9
77.4
53.8
57.7
46.2
27.9
37.5
21.5
66.4
15
3.4
215
8.4
175
375
55.0
72.3
68.6
76.4
74.3
74.0
622
64.3
505
53.6
42.6
63.9
12
-------
Table 4. EFFECT OF TEMPERATURE ON THE EXTRACTION OF PAHS
FROM SOIL 2 USING 5% METHANOL IN SUPERCRITICAL CO,
Experimental Conditions:
I Tcst# j 14 16
(Flow rate (ml/min)
(Extraction Time (mi...
! 17
4
18 J
i
50 j
fTcinpcratyre (CQ j 45 | 60
(Pressure (psi)
|%me-OH in CO2
2000
| 100
'
140 j
2020 |
5 j
Experimental Results:
PAH (mg/kg soil) Removed From Soil 2
Compound
Naphthalene
Accnaphthylcne
Acenaphthene
Fluorcnce
Phczianthrcnn
Anthracene
Fluoranthene
Pyrer.e
Bc.nz(a)anlhraccnc
Chryser.e + Triphenyle...
3cnzo[b)fluoranthe.ne
3cnzo(k)fluoranthene
8e.nzo(a)pyrene
^ndono(l,2,3-cd)pyrene
Dibenz(a,h)anthracene
3enzo(ghi)pery!ene
PAH#
1
2
3
4
5
6
7
8
9
10
n
12
13
14
15
16
Soil
23.4
51.6
95
45
26.9
26.2
242
318
127
12S
54.6
715
113
39.8
14.4
45.1
Test*?
14
C.9
8.9
0.9
0.9
12.4
16.7
210
258
104
99.1
29.4
41.8
522
11.1
5.4
9.7
16
05
12
0.5
0.9
25
23.3
230
280
120
119
38.7
54
70.6
16.1
7.6
13.9
17
0.9
3.6
0.9
0.9
18
19
211
252
65.3
602
14.8
17.3
21.1
2.9
1.8
23
18
0.7
5.9
0.7
0.9
50.3
355
246
2S5
75.3
695
16.8
19.8
235
2.8
1.4
2.4
13
-------
Table 4 (continued). EFFECT OF TEMPERATURE ON THE EXTRACTION OF
PAHS FROM SOIL 2 USING 5% METHANOL IN SUPERCRITICAL CO,
Data Analysis:
PAH Percentage Removal USing 5% Methanol in Supercritical CO2 at 45°C, 60°C, 100°C, and 140 °C
Compound
Naphthalene
Acenaphthylcne
JAcenaphther.e
iRuorcncc
iPhenanthrene
Anthracene
IFluoranthenc
Pyrene
Benz(a)anthracene
Test*
PAH# | 14
1 1
2
3
4
5
6
7
8
9
Chryscnc •*- Triphenyle... |j 10
Benzo(b)fluoranthene
Benzo(k)fhioranthene
Benzo(a)pyrene
[ndeno(l,2,3-cd)pyrene
Dibenz(a,h)anlhracene
Benzo(ghi)perylene
11
12
13
14
15
16
Total PAH Removal % |
3.8
172
9.5
20.0
46.1 •
63.7
86.8
81.1
81.9
77.4
53.8
57.7
46.2
27.9
375
215
66
16
2.1
233
5.3
20.0
919
88.9
95.0
88.1
945
93.0
70.9
745
625
405
52.8
30.8
78
17
3.8
7.0
9.5
20.0
66.9
725
872
792
51.4
47.0
27.1
13.9
18.7
7.3
125
5.1
53
18
3.0
11.4
7.4
20.0
187.0
137.0
101.7
89.6
59.3
543
30.8
27.3
20.8
7.0
9.7
5.3
65
14
-------
-D- 6.25 min, 4 ml/mm, 45 °C
-•- 6.25 min, 4m)/niin,145 °C
9 10 11 12 13 14 15 16
3 4
PAH#
Figure 2. PERCENTAGE REMOVAL OF PAHS FROM SOIL 1
15
-------
mol PAH/mol CO2
1.4E-6
-n- 6.25 min, 4ml/min, 45 °C
-•- 6.25 min, 4ml/inin. 145 °C
10 11 12 13 14 15 16
PAH#
Figure 3. NUMBER OF MOLES OF PAHS EXTRACTED
FROM SOIL 1 PER MOLE OF CO,
16
-------
Total mol PAHs/mol CO2
5.1E-6 -4
4.1E-6 -
3.1 E-6 -
2.10-6 -
1.1E-6 -
S.OE-8
4 ml/min
Ji5 C
4 ml/min
45 C
1.5 ml/min
45 C
0.5 ml/min
45 C
50
Extraction time (min)
75
Test 1
Test 2
Test3
Test 4
Test 5
Test 6
Test 7
100
Figure 4. EFFECT OF EXTRACTION TIME ON THE TOTAL EXTRACTION
EFFICIENCY OF PAHS FROM SOIL 1 AT DIFFERENT FLOW
RATES AND TEMPERATURES
17
-------
Considering these two rate limiting steps one should expect to observe a sharp decrease in
the slope of the mole fraction curve for short extraction times (when deposited PAHs are being
extracted) and a small decrease in the slope of the same curve for longer extraction times. Tests
8 through 12 were conducted at 4 ml/min of supercritical C02 at 45°C and 2000 psig for different
extraction times on a soil with 1296 mg/kg PAH concentration. In Figure 5. the moles of PAHs
per mole of C02 declines fairly rapidly for extraction times up to about 25 minutes. From 25 to
100 minutes, the extraction efficiency decreases more slowly. These results are consistent with
those of Tests 1 through 7, which were conducted on a different soil and different flow rates and
temperatures.
In Figure 6. the efficiency of extraction of each individual PAH compound decreases with
increasing extraction time from 6V* to 100 minutes. The total (cumulative) percentage removal
of PAHs increases with extraction time. The increase is fast initially (for short extraction times)
and continues to increase with a smaller slope for longer extraction times (Figure 7).
The addition of methanol as a modifier always enhances extraction of heavier PAHs
(PAH numbers 7 through 16) from soil. A high concentration of methanol (ten percent) in the
C02 enhances the extraction of fluoranthcne (No. 7) and heavier PAHs while reducing the
extraction of lighter PAHs. A low concentration of methanol (three percent) in supercritical CO,
enhances the recovery of both heavy and light PAHs (Figure 8).
For the same concentration of methanol (five percent) in supercritical C02. increasing the
temperature from 45° to 60°C enhances the extraction of PAHs from soil. Increasing the
temperature to 100° and higher (140CC) decreases the extraction efficiency (Figure 9).
Laboratory-Scale Tests
Tests 19 through 25 were conducted in the SCH laboratory-scale equipment in C02
recirculation mode. The results of these tests are presented in Tables 5 and 6. For Tests 19
through 21, the soils were analyzed for a suite of 16 PAHs; for Tests 22 through 25, the soils
were analyzed for Total Petroleum Hydrocarbons (TPH). The following conclusions can be
drawn from these experimental results.
The results shown in Figure 10 indicate that increasing die temperature from 110° to
155°F (43° to 68°C) and the pressure from 1700 to 1850 psi increases the percentage removal of
PAHs from soil (compare Tests 19 and 20). At the same temperature (155°F or 68°C),
increasing the pressure from 1850 to 2025 psi with a higher COVsoil ratio also increases PAH
removal (Tests 20 and 21).
In Figure 11, the results show that the efficiency of capturing PAHs on the activated
carbon increases by reducing the temperature of the activated carbon bed. At adsorption
temperatures of 145° and 155°F (63° and 68°C) (Tests 21 and 20, respectively), PAH capture is
fairly low. At an adsorption temperature of 110°F (43°C) (Test 19), PAH capture is significantly
increased. For the activated carbon used in these experiments (Sargent-Welch 8-12 mesh
18
-------
Total mol PAHs/mol CO2
2.0E-6-
1.5E-6 -
l.OE-6 -
5.1E-7 -
l.OE-8
25 50
Extraction time (min)
75
100
Figure 5. EFFECT OF EXTRACTION TIME ON THE TOTAL
EXTRACTION EFFICIENCY OF PAHS FROM SOIL 2
(Extraction conditions - 4 ml/min. 45°C, 2000 psi)
19
-------
gmol PAH/gmol CO2
5.0E-7
4.0E-7 .
3.0E-7 .
2.0E-7 -
l.OE-7 .
O.OE+0
1 234567
9 10 11 12 13 14 15 16
PAH#
Figure 6. EFFECT OF EXTRACTION TIME ON THE
EXTRACTION EFFICIENCY OF PAHS FROM SOIL 2
(Extraction conditions - 2000 psi, 45°C, 4 ml/min)
20
-------
% Removal
60-r
50-
40-
30-
20-
1 0-
25
50
Extraction time (min)
75
1 00
Figure 7. EFFECT OF EXTRACTION TIME ON TOTAL
PERCENT REMOVAL OF PAHS FROM SOIL 2
(Extraction conditions - 2000 psi, 45°C, 4 ml/min)
21
-------
Removal %
D 5% me-OH
o- no me-OH
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
50 -
Figure 8. EFFECT OF CONCENTRATION OF METHANOL
ON THE EXTRACTION OF PAHS FROM SOIL 2
(Extraction conditions - 2000 psi, 45DC, 4 ml/min)
-------
Remova]
120
45°C .D. 60°C •. 100°C o 140°C
100 -
80 -
'C'
60 -
40 .
r /
: /
//
i//
it
\
20 -
1
r °
2 3 4 5 6 7 8 9 10 11 12 13 14 15
PAH#
1
16
17
Figure 9. EFFECT OF TEMPERATURE OK PERCENTAGE
REMOVAL OF PAHS FROM SOIL 2
(Extraction conditions - 2000 psi, 4 ml/min. 5 wt % methanol in CO2)
23
-------
Table 5. RESULTS OF SUPERCRITICAL C02 EXTRACTION
TESTS CONDUCTED IN CO2 RECIRCULAT1ON MODE
Experimental Conditions:
Weight dry soil (gm)
Weight dry carbon (gm)
Extraction temperature (°F)
Extraction pressure (osi)
Adsorption temperature (°F)
Adsorption pressure (psi)
Extraction time (min)
Ratio of CO2/soil (scf /gm)
Activated carbon
Test#
19
: 26.1
: 12.4
110
1700
110
1700
50
1.214
20
30.9
11.9
155
1850
145
1850
60
1.034
21
34.7
112
155
2023
155
2025
64
1.672
GAC (Surgenl-Welch), Cocoanul, 8-12
Experimental Results:
Concentration of PAHs (mg/kg) Remained in Soil and Activated Carbon After Each Experiment
Compound
Naphthalene
Acer.aphthylcne
Acenaphthene
Fluorence
Phenanthrene
Anthracene
iFluoranthene
iPyrene
IBer.z(a)anthracenc
Chrysene + Triphenylene
Benzo(b)fluoranthene
Bcnzo(k)nuoranthcne
Bertzo(a)pyrene
Indcno(l,2,3-cd)pyrcne
Dibenz(a,h)anthracene
Benzo(ghi)pery]cne j
Total (mg/kg soil) j
IPAHtf
| i
2
I 3
4
5
6
7
8
9
10
11
12
13
14
15
16
Soil 3"
46.0
109.6
175
14.3
1205
82.9
198.7
251.1
123.4
138.0
66.1
76.9
1332
62.6
19.2
70.2
1530.1
1
Soil
38.70
60.40
2.70
9.40
62.30
38.20
175.00
224.00
122.00
136.00
66.00
76.80
133.00
61.90
17.80
69.50
1293.70
9
AC
15.30
1C2.00
31.10
8.90
107.00
34.30
42.70
44.50
1.40
180
030
0.30
0.4C
0.00
0.00
0.00
391.00
Tes
2
Soi1.
16.02
44.43
0.91
2.95
2955
21.48
125.11
176.93
120.57
130.57
61.70
72.05
121.14
53.98
21.14
59.77
1058.30
t #
0
AC
36.33
124.29
56.42
52.14
| 129.8C
42.14
57.22
53.33
1.76
2.13
0.19
0.19
0.00
0.00
0.00
0.00
555.93
1 2
Soil
| 7.33
I 35.67
\ 0.67
1.00
7.44
9.78
35.33
53.44
49.56
62.33
42.00
48.44
89.11
50.56
14.56
57.11
564.33
1
__££_!
42.45
123.24
61.67
69.22
100.88
33.14 '
69.3! :
56.14
3.17 j
3.66 j
0.59
0.4C !
G5Q
0.20
0.20
0.20
564.94
' Calculated based on PAK's left in the system and CO2.
24
-------
Table 5 (continued). RESULTS OF SUPERCRITICAL CO, EXTRACTION
TESTS CONDUCTED IN C0: RECIRCULATION MODE
Data analysis:
Percentage of Extracted PAH's Adsorbed on Activated Carbon From Soil 3
Compound
Naphthalene
Acenaphthylene
Acenaohthene
Fluorcnce
Phenanthrene
Anthracene
Fluoranthcne
Pyrene
Benz(a)anthracene
Chrysene + Triphenyler.e
Benzo(b)fluoranth.ene
Benzo(k)fluoranthene
Bcnzo(a)pyrcnc
Indenod ,2,3-cd)pyrene
Dibenz(a,h)anthracene
Benzo(ghOperylcne
PAH#
1
2
3
4
5
6
7
Test*
19
100
99
100
86
87
36
86
8 | 78
9 (I 49
10 j) 66
11 * 100
12 i
ICO
13 j 100
14 | 0
15 j 0
16 j 0
20
21
46.72 | 35.46
73.50
131.16
176.60
54.98
26.42
29.95
27.70
24.25
10.99
1.61
1.46
0.00
0.00
-0.00
0.00
53.S3
118.41
167.65
28.31
14.63
13.69
9.17
1.39
156
0.79
0.45
036
053
138
0.49
PAH's Percentage Removal From Soil 3
Compound
Naphthalene
Acenaphthylene
Acenaphthcne
Fluorence
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Bcnz(a)anthracene
Chrysene + Triphcnylcnc
Ben7.o(b)fluoranthene
Benzo(k)fiuoranthene
Benzo(a)pyrene
Indeno(l,2,3-cd)pyrcne
Dibcnz(a,h)anthracene
Benzo(ghi)perylene
Total PAH Removal, %
PAHS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Test*
19
15.8
44.9
845
344
4&3
53.9
11.9
10.8
1.1
15
02
02
0.1
1.1
73
1.0
15.5
20
65.1
59.4
94.8
79.4
755
74.1
37.0
295
2J
5.4
6.7
6.4
9.0
13.8
-10.1
145
21
84.0
67.4
96.2
93.0
93.8
88.2
8Z2
78.7
59.8
54.8
365
37.0
33.1
192
24^
18.6
30.8 j 63.1
25
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Table 6. EXTRACTION OF PETROLEUM HYDROCARBONS
FROM SOIL IN CO, RECIRCULATION MODE
Experimental Conditions:
Weight dry soil (gin)
Weight dry carbon (gm)
Extraction temperature (°F)
Test*
22
34.6
133
160
Extraction pressure (psi) || 1900
Adsorption temperature (°F) | 155
Adsorption pressure (psi) j, 1900
Extraction time (mini j! 60
Ratio of CO2/soil (scf/gm)
1.488
% of me-OH in Soil j 0
23
33.1
13.4
175
2000
170
2000
47
1.099
7.2
24
14.9
55
180
1930
132
1930
30
25
16.68
6.33
150
1880
165
1880
30
1.68 I 1.378
0 [ 0
Experimental Results:
Total petroleum concentration (mg/kg)
Soil before extraction
Soil after extraction
Activated carbon after extraction
17900
8500
3400
17900
8100
3200
17900
10500
5600
17900 |
8900 j
3400 i
Data Analysis:
JTPH extracted /mol CO2 (mg/mol)
(Percentage of Extracted TPH Adsorbed on AC
[Total % TPH removal
5.0
13.9
52.5
| 7.1 i
35 [ 5.2
j 132 I) 27.9
54.7
41.3
1 14.3
503
26
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10 11 12 13 14 15 16
O.OE-4) -
-2.0E+1
Figure 10. REMOVAL PERCENTAGE OF PAHS FROM
SOIL 3 IN RECIRCULATING MODE
(Extraction temperature in Tests 20 and 21 are the same. Higher
removal percent in Test 21 is due to higher ratio of C02 to soil)
27
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Percentage of Recovery
1234
PAHft
Figure 11. PERCENTAGE OF EXTRACTED PAHS
ADSORBED ON THE ACTIVATED CARBON
(At lower temperature, PAHS are adsorbed
better on the activated carbon)
28
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granular activated carbon from coconut shells), the percentage recovery was very sensitive to the
temperature of the activated carbon bed.
Tests 22 and 23 were conducted to determine the effect of modifier (mcthanol) on
extraction of TPHs. Addition of methanol to the soil directly (before extraction) increased the
ratio of TPHs extracted from soil to the number of moles of CCX, from 5.0 mg/mol to 7.1 mg/mol.
The ratio of TPH extracted by supercritical CO2 to TPH adsorbed by activated carbon was
slightly decreased by addition of methanol (Table 6).
The results of Tests 24 and 25 show the effect of activated carbon bed temperature on the
adsorption power of activated carbon. The data indicates that organic contaminants capture (as
measured by TPH) is improved using supercritical C02 at lower temperatures.
SELPhQx Field Test Unit
The overall objective of this task was to build a field test unit (FTU) based on the
SELPhOx process. This task was comprised of subtasks to design, construct, and conduct initial
shakedown testing of the FTU. For the FTU, the original SELPhOx process concept was
simplified to reduce the number of pressure vessels and process complexity.
The SELPhOx FTU design incorporated C02 recirculation in the SCE stage, contaminant
collection in an activated carbon vessel, and a wet air oxidation (WAO) reactor with off-gas
condenser. Contaminant-laden activated carbon from the contaminant collection vessel was
collected after each SCE cycle. The activated carbon was weighed and manually loaded into the
WAO vessel and slurried with a weighed quantity of water. High-pressure cylinders provided air
for the WAO reactor. Temperatures in each vessel were controlled by local temperature
controllers and recorded by a dedicated computer-based data acquisition system. Means for
adding modifiers, such as alcohols, to the SCE stage could be provided in the FTU. Also, high-
pressure cylinders containing liquid C02 blended with a small amount of modiiier could be used
as in the laboratory-scale batch tests.
As the FTU is an experimental unit, several aspects of a commercial-scale plant are not
included. In a commercial unit, after each extraction cycle is completed, supercritical CO2 is
pumped to a high-pressure holding tank for the next cycle. The C02 is not depressurized during
the process, which saves considerable expense in recompression. Also in the commercial design.
CO2 is separated from the WAO product gas and recycled to the supercritical extraction cycle.
Separation and recycle of regenerated activated carbon from the WAO unit is an important
consideration of the commercial design. However, at this stage of process development, we do
not consider this necessary to demonstrate the SELPhOx process.
The FTU was constructed and installed at IGT's Research Center in Des Plaines, Illinois.
The base and frame for the FTU is constructed of high-strength Unistrut® beams. The FTU floor
is made from %-inch thick plywood. The nominal dimensions of the FTU are 5'/z feet wide by 6
feet tall by 8 feet long. The computer, controls, supercritical extraction unit, activated carbon
vessel, and high-pressure recirculation pump are positioned along one side of the frame. The
29
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WAO unit as well as CO, and air cylinder storage are on the other side of the FTU frame. Three-
phase (220 V) power is required lo operate the high-pressure piston pump for initially charging
the CO, to the extraction unit. Single-phase (115V) power operates the computer, strip-chart
recorder, line and vessel heaters, temperature controllers, and pressure transducers.
In the WAO vessel, a backpressure regulator (BPR) controls air pressure. The BPR is set
manually for the desired pressure. The oxidizer pressure is monitored and recorded by the
computer. A mass flow controller (MFC) is used to control the flow rate of the air into the
WAO. A check valve installed after the MFC ensures one-way flow of air into the oxidizer. The
air is introduced from the bottom of the oxidizer through a simple sparger. An agitator is used to
continuously mix the slurry of activated carbon and water. Two graphite-impregnated gaskets
are used to seal the head of the oxidizer vessel and maintain pressure. An electric heater heats
the oxidi/er vessel. A local temperature controller controls temperature.
Product gas from the oxidizer consists predominantly of C02. nitrogen (from sparged air).
and water vapor. This effluent flows to a condenser where the bulk of the water vapor is
removed from the stream. An in-line check valve ensures one-way flow of product gas to the
condenser. The level of accumulated water in the condenser (which also acts as a reservoir) is
observed by a visual level indicator. A pressure regulator controls the pressure of the reservoir.
Cooled effluent gases exit the WAO unit from the top of the condenser. Condensed water is
recirculated to the WAO vessel by a metering pump as needed.
For the temperature control circuits in the supercritical extractor and wet air oxidizer, a
solid-state relay was added to accommodate the electric current requirement of the heaters. For
the temperature control circuit for the extractor vessel lines, the built-in capacity of 21/: amps was
sufficient. Since computer records the temperatures, the output from each thermocouple is sent
in parallel to the data acquisition system and to the temperature controller.
The main components of the WAO unit include the oxidizer vessel, heater, connecting
lines, air sparger, condenser, reservoir, pressure control system, temperature control system,
heater, blanket insulation, make-up water pump, agitator and variable-speed motor, and level
indicator. A motor for the agitator, mass flow controller for air, and air pressure control system
were also installed.
A condenser to condense water vapor exiting the WAO was installed downstream of the
BPR. The condenser was constructed as two sections: 1) a shell-and-tube heat exchanger with
vapor on the shell side and chilled fluid on the tube side, and 2) a vertical cylindrical vessel with
a cooling coil wrapped around its upper part. The heat exchanger is constructed using '/4-inch
stainless steel tubing with '/i-inch stainless steel tubing for the shell. The cooling coil for the
cylindrical vessel was constructed with !/4-inch copper tubing.
The chilled fluid (ethylene glycol) enters the heat exchanger at -9°C. The cold fluid
leaving the heat exchanger enters the cooling coil of the cylindrical vessel. The effluent from the
oxidizer, which consists essentially of water vapor and CO,, enters the heat exchanger at about
250°C. Most of the water is expected to condense in the heat exchanger; the remaining water
30
-------
will condense in the vessel, which is cooled at the top. The condensed water is collected in the
lower half part of the vessel. The level of the water in the vessel is observed through a glass
sight tube, which is installed in parallel with the vessel.
Cylinders of liquid CO2 provided the on-board supply of fluid for supercritical tests.
Cylinders of high-pressure air provided air for the WAO stage. Utilities included electricity,
water, and instrument air.
Field Test Unit and DataAnalysis
The objectives of this task were to conduct integrated supercritical extraction/liquid-phasc
oxidation tests with contaminated soils using the SELPhOx F'l'U and to analyze the data
generated during these tests. Operating eonditions were based on laboratory-scale tests results.
The results of the three shakedown tests conducted in the FTU are summarized in 'fable 7
below. The tests were conducted with contaminated soil containing from 3200 to 3400 mg/kg of
TPII (total petroleum hydrocarbons). The nominal conditions for the tests were a system
pressure of 2000 psig, extraction temperature of 70° to 82°C, absorption temperature of 68° and
71°C, and extraction time of 1 to 2 hours. The ratio of activated carbon in the absorption vessel
to the quantity of contaminated soil charged to the extraction vessel was 1 to 3 (wt/wt).
Table 7. SUMMARY OF CONDITIONS AND RESULTS OF SHAKEDOWN
TESTS CONDUCTED IN THE SELPhOx FTU WITH CONTAMINATED SOIL
Test No. 123
Feed, grams 2911.5 3000 1932.7
TPH Concentration, mg/kg 3400 3300 3200
Moisture Content, wt %. 9 12 11
Pressure, psig 2000 2000 2000
Extraction Vessel Temperature, °C 70 82 71
Absorption Vessel Temperature, °C 68 71 71
Extraction Time, hours I 1 2
Soil/Carbon ratio, wt/wt basis 3 3 1
Extracted Soil, grams 2911.5 3000 1932.7
Concentration, mg/kg 2300 3000 2300
Moisture Content, wt %. 7 10 11
Activated Carbon, grams 998.2 1000 1933
Concentration, mg/kg 320 100 540
Moisture Content, wt %. 334
% Extracted from the soil 30.9 7.0 28.1
% Collected by the activated carbon 3.4 1.1 18.2
Overall TPH material balance, % 72.6 94.1 90.1
31
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The results of these shakedown tests show that TPH compounds were extracted from the
contaminated soil with the recirculating supercritical CO,. However, the extent of extraction was
lower than expected based on the results of the laboratory-scale tests. Extractions of about 30
percent were achieved in Tests 1 and 3. In Test 2, the extraction was less than 10 percent. The
temperature of the extraction does not appear to have affected the extent of extraction
significantly.
The quantity of the TPH compounds that were collected by the activated carbon was very
low. The best recovery was about 18 percent in Test 3. This test also had the highest ratio of
activated carbon to soil (1 wt/wt) than the other tests. It also had the lowest quantity of soil
charged to the extraction vessel (~2 kilograms). The quantity of soil charged and the ratio of
soil/activated carbon appear to have more impact on the results than the extraction and
absorption temperatures.
The results of the shakedown tests indicate two significant aspects of FTU operation that
require additional experimental confirmation: 1) the flow rate of supercritical CO, that is
actually being recirculated through the extraction vessel via the recycle compressor needs to be
quantified more rigorously. The flow meter readings taken during the tests indicate that
supercritical C02 was being recirculated through the extraction vessel. However, fluctuations in
the flow meter readings were significant which caused uncertainty in the accuracy of the flow
meter calibration. The supercritical CO-, flow meter calibration must be confirmed. 2) the flow
pattern of the supercritical C02 flowing through the bed of contaminated soil must be
determined. Supercritical C02 may have been flowing through the extraction cell at the
prescribed flow rate; however, it may have channeled through the contaminated soil in the bed
with much of the contamination not intimately contacting the C02. A supercritical CO2 flow
distributor may be required in the extractor as well as the activated carbon collector vessels.
Both of these factors may have contributed to the low extractions as well as the low carbon
collection by the activated carbon.
Wet Air Oxidation Tests
The objective of this task is to determine the effectiveness of wet air oxidation (WAO) on
destroying/degrading contaminants adsorbed onto activated carbon obtained from SCE. Up to
three samples will be subjected to WAO using a batch autoclave unit at IGT. Samples of
contaminant-laden activated carbon were generated in the FTU as described above. Results of
this work will be used to scale the WAO portion of the SELPhOx process and assist in a
preliminary materials evaluation. Results of this work will also be used to evaluate the
economics of the WAO portion of the SELPhOx process.
A shakedown test was conducted in the WAO unit installed on the SELPhOx FTU with
contaminant-laden activated carbon from supercritical extraction test No. 1. A 10 weight percent
slurry of the activated carbon sample and deionized water was prepared and charged to the WAO
vessel. Operating conditions for the WAO test were a nominal temperature of 240° to 250°C, a
pressure of 700 to 800 psig, and an air sparge (bubbling) rate through the WAO vessel of 6 to 7
-------
ml/minute. The slurry of activated carbon and water was held at conditions for one hour. The
activated carbon samples were analyzed before and after the WAO test. The extent of TPH
destruction via WAO for this shakedown test was about 15 percent. It appears that more severe
conditions will be required to accomplish the desired TPH destruction.
Process Design and Economics
A facility design and cost estimate was made for a transportable unit to process
contaminated soil from a typical site. The approach will be to size the SCR equipment for the
transportable unit to achieve a high degree of extraction of the principal organic hazardous
constituent (or POHC). Similarly, the WAO equipment will be sized for achieving a high degree
of destruction of the same POHC. The effect of lower or higher extraction and destruction
criteria on the economics of the transportable unit will be determined in parametric studies.
The overall objective of this work is to determine if the capital and operating costs of the
SELPhOx process are competitive with other soil remediation technologies with which it must
compete. The criterion of competitiveness for the process is soil remediation costs of less than
about $200 per ton. Further, in order to estimate the economics of the process, a fairly detailed
process design must be prepared. Problems and concerns that arise during the design process can
be addressed in a timely manner, rather than waiting toward the end of the project.
The total capital cost for a commercial-scale SELPhOx plant consisting of 3 supercritical
extraction trains and one WAO train with intermediate CO, storage was estimated for the project.
The nominal throughput capacity for a commercial-scale plant is 100,000 tons of soil per year.
The total plant investment for a SELPhOx plant lo process 100,000 tons per year of
contaminated soil was determined to be $16,300,000. Based on a 10-year equipment
amortization and 6.0 percent cost of capital, the yearly operating costs were estimated to be
59,333,000. This relates to a unit processing cost ranging from $150 to $250 per ton.
Project Management
The objective of this task was to ensure that a coordinated program is maintained among
the EPA and IGT, and that all program requirements are met.
During the project period, IGT oversaw the experimental and process design work of the
program. The University of Illinois (Chicago campus) participated in the project with the
involvement of a doctoral candidate under the tutelage of Professor G. Ali Mansoori. One paper
was prepared for the American Chemical Society meeting held in New Orleans on March 23-25.
1996. This paper was entitled "SELPhOx Process for Remediation of Contaminated Soil." A
second paper entitled "Design and Construction of a Supercritical Fluid Extraction Process for
Remediation of Contaminated Soil" was presented at the 1996 Midwest Thermodynamics and
Statistical Mechanics Conference held on May 3 (Madison, WI).
33
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CONCLUSIONS AND RECOMMENDATIONS
The following conclusions can be drawn from the experimental results
• The extent of PAH extraction from soil by supercritical C02 increases with temperature to a
maximum at about 65°C. At temperatures above 65°C the extent of PAH extraction
decreases.
• In PAH adsorption tests with activated carbon; the results showed that lower, rather than
higher temperatures of the activated carbon increased the capture of'PAHs from supercritical
CO2. A temperature of about 45°C yielded the highest recovery of PAHs.
• The results of tests conducted with modifier (mcthanol) showed that a concentration of three
percent yielded higher PAH extractions than any other higher methanol concentration (up to
10 percent methanol in CO, was tested).
It is recommended that the concerns described above for the operation of the SELPhOx
FTU be addressed and that additional supercritical CO, extraction and WAO tests be conducted
in the FTU to develop design data to scale up the FTU to commercial scale.
ACKNOWLEDGMENTS
The authors acknowledge the funding of this research project by the U.S. Environmental
Protection Agency through the Supcrfund Innovative Technology Evaluation program and IGT's
Sustaining Membership Program.
34
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NRMRT.-CIN N0889
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing,
1. REPORT NO.
EPA/60n/H-9Q/112
3. RE
4. TITLE AND SUBTITLE
Supercritical Extraction/Liquid Phase Oxidation of Wastes
5. REPORT DATE
December 1999
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
Michael C. Mensinger, Amir Rehmat, and Anil Goyal
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Institute of Gas Technology
1700 South Mount Prospect Road
Des Plaincs, IL 60018-1804
1O. PROGRAM ELEMENT NO.
TDIYIA
11. CONTRACT7GRANT NO.
CR822701
12. SPONSORING AGENCY NAME AND ADDRESS
National Risk Management Res I .ab IGT Sustaining Membership Proj
Office of Research and Development 1700 South Mount Prospect Rd
U.S. Knvironmental Protection Agency Des Plaines, IL 60018-1804
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final. 9/29/94-5/31/98
14. SPONSORING AGENCY CODE
bP A/600/14
15. SUPPLEMENTARY NOTES
Contact: Valdis R. Kukainis (513) 569-7955
16. ABSTRACT
During the experimental program, IGT conducted a series of laboratory-scale supercritical CO, extraction
tests to evaluate the effects of CO2 How rate, temperature, and the addition of a modifier on Ihe extraction
of polynuclcar aromatic hydrocarbons (PAHs) from soil. These tests were conducted in IGT's
laboratory- and bench-scale supercritical extraction equipment. The laboratory-scale tests were
conducted with supercritical CO2 in once-through mode. The bench-scale tests were conducted in CO,
rccirculalion mode with activated carbon adsorption of the PAHs. Overall, the results of these tests show-
that the extent of PAH extraction from soil increases with temperature to a maximum at about 65°C. At
temperatures above 65°C the extent of PAH extraction decreases.
In PAII adsorption tests with activated carbon, the results showed that lower, rather than higher,
temperatures of the activated carbon increased the capture of PAHs from supercritical CO, T A '
temperature of about 45°C yielded the highest recovery of PAHs. The results of tests Conducted with
modifier (Methanol) showed that a concentration of three percent yielded the highest PAH extractions in
the range of mclhanol concentrations, up to 10 percent in CO2.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Supercritical extraction, Liquid phase, Oxidation,
PAH adsorption tests, Activated carbon,
Hazardous waste, Contaminated soils
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
. SEC
21. NO. OF PAGES
41
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 {Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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