Determination of Anions in Fracking Flowback Water From the Marcellus Shale Using Automated Dilution and Ion Chromatography
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Determination of Anions in Fracking
Te ch ni cal N ote 1 3 9
Flowback Water From the Marcellus
Shale Using Automated Dilution
and Ion Chromatography
Carl Fisher, Richard Jack, and Linda Lopez
Thermo Fisher Scientific, Sunnyvale, CA, USA
Key Words
Dionex AS-AP Autosampler, Dionex IonPac AS18, Hydraulic Fracturing,
In-line Conductivity
Goal
Demonstrate the use of in-line conductivity measurement to trigger
automated dilution prior to separation and quantification of inorganic
ions and organic acids in Marcellus Shale fracking flowback samples
using ion chromatography.
Introduction
The rapid increase in U.S. natural gas production in
recent years has been propelled by the extensive use of
hydraulic fracturing (also known as fracking). This
process extracts natural gas by drilling into bedrock
(primarily shale) and then injecting fluid under high
Organic acids, such as acetate and formate, are added to
pressure causing cracks in bedrock, thereby releasing
fracking fluid to adjust the pH.6 The pH of fracking fluid
trapped gas that can be captured.1 Fracking fluid contains
is maintained within a narrow range to ensure the
approximately 85% water and 13% sand (proppant), the
effectiveness of surfactant additives that facilitate the
latter to prop open cracks, which facilitates the flow of
penetration of fracking solution into bedrock. These
gas. The remainder consists of chemical additives such
organic acids can act as a carbon source to promote the
as friction reducers, anti-bacterial agents, and corrosion
growth of anaerobic bacteria, resulting in the production
inhibitors. 2
of corrosive and toxic hydrogen sulfide. Additionally,
Fracking has been in use since the 1940s primarily for because not all of the fracking solution is recovered,
oil extraction, however recent refinements to this process bacteria can grow within the interstitial cracks following
have enabled the exploitation of energy resources that had a fracking event and block gas flow over the long term,
previously been inaccessible. 3 While fracking provides inhibiting well production. Thus, the concentration of
financial benefits to both local and national economies, organic acids should be closely monitored.
it has not been without controversy. Inadvertent spills or
The high levels of dissolved salts leached from bedrock
the dumping of fracking flowback (fracking solution that
are a challenge to analyzing fracking flowback solutions.
returns to the surface via the well bore) into unlined
Injection of high ionic strength solutions can exceed the
collection ponds can contaminate ground water.4
capacity of columns used in ion chromatography,
Additionally, high levels of chloride and bromide found resulting in poor chromatography, peak suppression
in fracking wastewater can result in effluent discharged (i.e., poor recovery), and inaccurate reporting. Additionally,
by wastewater treatment facilities that exceed the levels high concentrations may exceed the linear calibration
allowed in the facility’s discharge permits. 5 Chlorination range for a particular analyte. These samples require
or ozonation, as part of the purification process, can dilution prior to injection, which results in an additional
produce disinfection byproducts (DBP) such as bromate,
chlorate, and haloacetic acids. These DBPs are carcinogens
or interfere with human development and, consequently,
are regulated by the U.S. Environmental Protection
Agency’s National Primary Drinking Water Regulations.2
sample preparation step and the possibility of errors. To Reagents and Standards
minimize errors and reduce labor costs, there are a number • 18 MW-cm resistivity degassed deionized (DI) water
of options available to automate the determination of
• T hermo Scientific Dionex 1000 µS conductivity
the need for and then the loading of less sample:
standard (P/N 080172)
•T
he AutoDilution feature of Thermo Scientific™ • U ltra Scientific 1000 mg/L Certified IC Standards or
Dionex™ Chromeleon™ Chromatography Data System Fisher Scientific reagents, ACS grade
(CDS) software. If a chromatogram has an analyte
peak height or area that exceeds a pre-set limit, a Samples
smaller amount of sample is re-injected using either a: Fracking flowback solutions from the Marcellus Shale
a. Partial loop (F1–10) were collected from successively later times
b. Smaller loop during the fracking process.
c. V
ial to vial dilution using a Thermo Scientific
Conditions
Dionex AS-AP Autosampler
Chromatographic
• Measurement of sample conductivity prior to injection.
Columns: Thermo Scientific™ Dionex™ IonPac™
This can be done a) manually, which is tedious, labor
AG18/AS18, 4 mm
intensive, and prone to error, or b) automatically,
using the Thermo Scientific Dionex AS-AP Sample Eluent Source: Thermo Scientific Dionex EGC III KOH Cartridge
Conductivity and pH Accessory. If the conductivity Eluent: 23 mM or 39 mM KOH
exceeds a specified amount, Chromeleon CDS can
Flow Rate: 1.0 mL/min
trigger the loading of less sample as per a–c above.
Column Temp. 30 °C
These options are depicted in Figure 1 and are described
in greater detail in Technical Note 138.7 Inj. Volume: 25 µL
Detection: Suppressed conductivity, Thermo Scientific™
Dionex AS-AP
Dionex™ ASRS™ 300 Anion Self-Regenerating
Autosampler Suppressor*, recycle mode, 57 mA (23 mM
Fracking Sample
KOH); 97 mA (39 mM KOH)
Sample Conductivity
and pH Accessory Background < 2 µS
Conductance:
Centrifugation
IC System Noise: < 3 nS
Does conductivity No
exceed cutoff? System Backpressure: 2100 psi
Filtration
Yes Chromatogram * E quivalent or improved results can be obtained using the Thermo Scientific™ Dionex™
AERS™ 500 Anion Electrolytically Regenerated Suppressor.
Sample Dilution
Yes No
Does peak area
Report Dionex AS-AP Autosampler Dilution
or height exceed
cutoff? Syringe: 1 mL
Chromeleon AutoDilution
option required
Buffer Line Volume: 1.2 mL
Wash Solution: 18 MW-cm resistivity degassed DI water
Figure 1. Automated sample analysis options available using the Dionex AS-AP Autosampler and
from autosampler wash liquid reservoir
Chromeleon software.
Vials: 10 mL
This Technical Note describes the analysis of fracking
Dilution Volumes: 20 µL sample into 1980 µL DI water
flowback solutions using ion chromatography following
in-line determination of sample conductivity and Draw/Dispense Speed: 50/25 µL/sec (water)
automated dilution of high ionic strength samples. 10/5 (sample)
Mix by Shake Iterations: 10
Equipment
Carousel Speed: 30,000 encoder counts (maximum, default)
• T hermo Scientific™ Dionex™ ICS-2100 Integrated
Reagent-Free™ IC (RFIC ™) System with an additional
Dionex AS-AP Sample Conductivity and pH Accessory
10-port valve (P/N 069473)
Volume Drawn: 600 µL
• Dionex AS-AP Autosampler
Draw/Dispense Speed: 20/10 µL/sec
– Dionex AS-AP Sample Conductivity and pH
Part numbers of the consumables used in this document
Accessory (P/N 074923) with the included pH
are listed in Table 1.
electrode port plug and seal installed
• Chromeleon CDS, version 6.8 (release 6.80 DU11c
or later) or 7 (release 7.1 SR1 or later)3
Table 1. Consumables list. Dionex ICS-2100 IC
Reagent-Free System
Part Dionex AS-AP Autosampler
Product Name Description Regen
Number Fresh 18 MΩ-cm
Deionized Water
Dionex EGC III KOH Eluent generator
074532 Eluent In
ERS 500
CD
cartridge cartridge Suppressor
Thermo Scientific Continuously regenerated
060477
Dionex CR-ATC column anion trap column Syringe
Needle Columns
Dionex IonPac AS18 Separation column,
060549
column 4 mm i.d. Tray Carousel
Dionex IonPac AG18 Heat Fresh 18 MΩ-cm
Guard column, 4 mm i.d. 060551 Exchange Deionized Water
column Tubing Regen
Thermo Scientific™
Suppressor cartridge, Degas
CR-TC EGC III Pump*
Dionex™ AERS™ 500 082540 Module
4 mm i.d. columns Sample Loop
suppressor Backpressure
Coil
Polystyrene vials with Waste
Dionex AS-AP
caps and blue septa, 074228 Figure 2. Flow diagram for the Dionex ICS-2100 IC Reagent-Free System with 10-port valve.
Autosampler vials
10 mL, package of 100
Sample and Standard Preparation
Wash Liquid Line
Samples were centrifuged at 10,000 × g, 10 min to pellet
solid particles, which facilitated filtration. The resultant To Buffer Line
Syringe
supernatant was filtered with a 0.2 µm polyethersulfone Syringe Waste Line
(PES) syringe filter. Samples were diluted as required Wash
Reservoir
with degassed 18 MW-cm resistivity DI water.
Sample Conductivity
Eluent Eluent
It is important to use 18 MW-cm resistivity, DI water for and pH Accessory
In Out
eluent and autosampler flush solutions to avoid system
contamination, decreased sensitivity, and poor calibration.
Degassing the DI water by vacuum filtration prior to use Accessory
Inlet Line
is a good laboratory practice.
Auxiliary Valve 3 2
Standards were prepared by diluting Certified IC Standard Bypass Line
4 1
stock solutions or by dissolving ACS grade reagents with Accessory
Waste Line 5 6
DI water.
Auxiliary Valve
Instrument Setup and Installation Sampling Needle (B Position)
Install, hydrate, and condition the Dionex EGC III KOH
L
eluent generator cartridge. This cartridge requires at least Carousel 5 4
2000 psi of backpressure for optimal operation. Install
W 6 3 C
and hydrate the Dionex CR-ATC trap column and the
12
Dionex AERS 500 Anion Electrolytically Regenerated L P
Suppressor. Figure 2 outlines the flow path of the standard Injection Valve
Dionex ICS-2100 system setup with a Dionex AS-AP Injection Port Sample Transfer Line (Inject Position)
Autosampler. Hydrate the devices and finish the system
setup according to the product manuals and the Dionex Figure 3. Dionex AS-AP plumbing schematic for Push Mode with a Sample Conductivity and pH Accessory.
ICS-2100 Operator’s Manual.8–12 Install and condition the
column using the conditions described in that column’s
Quality Assurance Report (QAR) for 30 min prior to
installing them in-line with the suppressor. If total
system backpressure is < 2000 psi, install one or more
backpressure coils between the Dionex CR-ATC
Continuously Regenerating Anion Trap Column and
the injection valve to increase the system pressure to
2000–3000 psi.
Install the Dionex AS-AP Sample Conductivity and
pH Accessory in the Dionex AS-AP Autosampler as
outlined in the Accessory Setup and Operation Guide.13
Figure 3 depicts the setup required for Push mode with
this accessory.4
For the experiments presented here, the 10-port valve of Columns: Dionex IonPac AG18/AS18, 4 mm
Eluent Source: Dionex EGC III KOH cartridge
the Dionex ICS-2100 system was used as the auxiliary Eluent: 39 mM KOH
valve. Alternatively, if the optional high-pressure valves Flow Rate: 1 mL/min
Inj. Volume: 25 µL
are installed in the Dionex AS-AP Autosampler, they can
Col. Temp.: 30 °C
be used to divert sample to the Dionex AS-AP Sample Detection: Suppressed conductivity, Dionex ASRS 300 Suppressor,
Conductivity and pH Accessory. Install the pH electrode recycle mode
Sample: 100-fold fracking flowback, filtered, 0.2 µm
port plug, which reduces the amount of injected sample
from 2000 to 600 µL for conductivity determination. Prior Peaks: Measured Undiluted
1. Acetate < 0.05 mg/L5
Column: Dionex IonPac AG18/AS18, 4 mm
Eluent: 23 mM KOH 350
Flow Rate: 1 mL/min
300
Inj. Volume: 25 µL
Col. Temp.: 30 °C 250
Area ( µS*min)
Detection: Suppressed conductivity, Dionex ASRS 300 Suppressor,
recycle mode 200
Sample: A. Standard 2
150 r = 1.00
B–E. 100-fold fracking flowback F1, F2, F5, and F10, filtered,
0.2 µm %RSD= 1.12
100
Peaks: A
1. Fluoride 0.5 mg/L 50
2. Acetate 2.5
0
3. Propionate/Formate –
4. Formate 1.0 0 200 400 600 800 1000 1200 1400 1600 1800 2000
4.8 Concentration (mg/L)
Figure 6. Chloride standard curve.
1
2 3 Change in Ion Concentrations During Fracking
4 As fracking progresses, the level of anions in flowback water
changes. As can be seen in Figures 7 and 8, chloride and
bromide concentrations increased ~10-fold from the first
to the second fraction and then, in subsequent fractions,
showed a slower, but steady increase. This result suggests
µS that, as fracking proceeds, progressively more of these ions
are dissolved into the flowback solution from the bedrock.
A
Conversely, the concentration of acetate decreased sharply
B and then remained at low levels from fraction two onwards.
These elevated concentrations would increase the amount
C
of processing required by water treatment facilities. In a
D similar manner, what appears to be propionate (or a
mixture with formate) in the first fraction is no longer
E
present in measureable quantities in subsequent fractions.
0 In contrast to the other analytes quantified, the level of
2.5 3 3.5 4 sulfate remained relatively constant, averaging 13 mg/L.
Minutes
100,000
Figure 5. Comparison of early eluting inorganic anion and organic acids in 90,000
fracking flowback water. 80,000
70,000
Concentration (mg/L)
Chloride Standard Curve Determination 60,000
One concern with using concentrated samples is that the 50,000
conductivity measured for an analyte will be outside of 40,000
the linear quantification range. For the wastewater samples 30,000
20,000
analyzed in this Technical Note, the primary analyte for
10,000
which this situation might arise is chloride. To confirm
0
that the concentrations of diluted samples were within F1 F2 F3 F4 F5 F6 F7 F8 F9 F10
the linear range for chloride, a standard curve was Fraction
generated. As can be seen in Figure 6, the standard curve Figure 7. Concentration of chloride in fracking flowback samples.
obtained was linear from 1–2000 mg/L with an r2 of 1.00
1,000
and %RSD of 1.12. This result indicates that even a
sample solution containing 200,000 mg/L of chloride, if 900
diluted 1:100, would still fall within the range for which 800
an accurate calculation of concentration can be obtained 700
for this analyte. 600
Concentration (mg/L)
500 Bromide
400 Acetate
300 Sulfate
200 Formate
100
0
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10
Fraction
Figure 8. Concentration of inorganic anions and organic acids in fracking
flowback samples.One explanation for the apparent decrease in acetate References
Te ch ni cal N ote 1 3 9
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As shown in Table 2, the recovery of acetate was 114 2. Bomgardner, M. Cleaner Fracking. C&EN, 2012,
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particularly for fraction 10, which had the highest Drinking Water Resources: Progress Report;
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the amount present in fracking flowback water samples Washington, DC, 2012.
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4. O
nishi, N. Fracking Tests Ties Between California
‘Oil and Ag’ Interests. New York Times, June 2,
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www.thermoscientific.com/dionex
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