Research Note
pubs.acs.org/IECR
Crude Oil Sorption by Raw Cotton
Vinitkumar Singh,† Ronald J. Kendall,† Kater Hake,‡ and Seshadri Ramkumar*,†
†
Nonwovens & Advanced Materials Laboratory, Texas Tech University, Lubbock, Texas 79409, United States
Cotton Incorporated, Cary, North Carolina 27513, United States
‡
S Supporting Information
*
ABSTRACT: Since the recent Deepwater Horizon Gulf of Mexico oil spill, the need for environmentally friendly oil sorbents
has intensified. This study deals with the sorption of crude oil by raw cotton, a biodegradable sorbent. To our best knowledge,
the data related to crude oil sorption by unprocessed raw cotton and correlation with cotton characteristics such as micronaire,
fineness, and maturity are unavailable. More importantly, our work quantifies the oil sorption (g/g) of low micronaire
(immature) cotton. Results showed at the minimum level, low micronaire raw cotton has 30.5 g/g crude oil sorption capacity.
Furthermore, the crude oil sorption capacity of low micronaire cotton was significantly higher than the sorption capacity of high
micronaire cotton. Brunauer−Emmett−Teller (BET) surface area and environmental scanning electron microscopy analyses
support the correlation between the quality characteristics of raw cotton and its oil sorption capacity. In contrast to synthetic
sorbents, raw cotton with its high crude oil sorption capacity and positive environmental footprint make it an ecologically friendly
sorbent for oil spill cleanups.
oil sorption by raw cotton and also correlates the crude oil uptake
capacity with its characteristics such as micronaire, fineness, and
maturity. Our result shows that low micronaire cotton, because of
its finer structure and wax content, can absorb higher amounts of
oil than regular-grade cottons. In addition, the basic mechanism
behind the sorption of crude oil by raw cotton was investigated
based on Brunauer−Emmett−Teller (BET) surface area and
environmental scanning electron microscopy (ESEM) analyses.
INTRODUCTION
Oil spills have caused significant environmental and ecological
problems.1 Effective decontamination and cleanups are
necessary after the spill for the protection of environment
and human health. Effective sorbent for an oil spill cleanup
should have important characteristics such as oleophilicity,
hydrophobicity, oil retention capacity, reusability, and biodegradability.2−4 Although there are currently many cleanup
technologies, such as in situ burning and the use of chemical
dispersants and sorbents (such as booms and skimmers), the
development of environmentally friendly sorbents that have less
logistic burden in usage and biodegradable are needed. In addition,
availability and economic feasibility plays an important role in the
selection of a sorbent material for cleanup operation.5,6 For the
efficient application of sorbents, data on the sorbent sorption
capacity and a good understanding on the basic mechanism
behind their sorption capability are needed. Although many
researchers have extensively investigated natural fibers (such as
kapok, barley straw, and wool),4,7−9 synthetic polymers,2,3,10,11 and
cellulose-based materials12−14 as potential sorbents for oil spill
cleanup, data over the sorption capability of these sorbents using
crude oil have not been reported. In addition, only a few studies
have addressed the mechanism of oil takeup by such materials.4,15
A clear and thorough understanding on the basic mechanisms
governing oil uptake in cellulose-based materials, particularly
cotton, is unclear and very limited.
In this study, we report the sorption capacity and the
mechanism behind the crude oil sorption of low micronaire
(immature) cotton. Micronaire of a cotton fiber relates to its
fineness and maturity. Fineness represents the linear density of
fibers (measured in millitex) and maturity defines the degree of
cellulose deposition (cell-wall development).16 The lower the
micronaire of a cotton fiber; the lower its maturity, the higher its
surface wax content, and the finer the fiber.17 Low micronaire
cotton has less use value and is discounted economically. To the
best of our knowledge, this study is the first to report the crude
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© 2013 American Chemical Society
EXPERIMENTAL SECTION
Raw cotton fibers used in this study were procured from Kitten
Land Company (Slaton, TX). The unprocessed raw cottons
used in this study are different from the material used by Choi
and Cloud.18 Characterization of cotton samples for fiber
characteristics such as micronaire, fineness, and maturity was
carried out at Texas Tech University’s Fiber and Biopolymer
Research Institute, using cotton quality testing instruments
such as the Uster High Volume Instrument (HVI) and the
Uster Advanced Fiber Information System (AFIS). Raw crude
oil used in this study was obtained from Midland, TX. The
characteristics of raw crude oil at 25 ± 1 °C and a relative
humidity (RH) of 63% ± 2% were as follows: viscosity = 30 cP,
density = 0.97 g cm−3, and surface tension = 30.39 mN m−1.
Oil Sorption Testing Method. Oil sorption capacity of raw
cotton was measured using a slightly modified method based on the
ASTM Standard F726-06 test method for the sorbent performance
of adsorbents (see Figure 1).19 Raw cotton (0.5−0.6 g) was placed
in a circular stainless steel mesh and immersed in a glass dish filled
with 1500 mL of raw crude oil, such that the circular mesh floated
freely in the oil. After the sample was positioned, the dish was
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Received:
Revised:
Accepted:
Published:
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April 25,
23, 2013
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dx.doi.org/10.1021/ie4005942 | Ind. Eng. Chem. Res. 2013, 52, 6277−6281
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Figure 1. Crude oil uptake by raw cotton.
covered with the glass plate. The entire system was placed over a
shaker table and was shaken at 75 rpm for 15 min to create a
dynamic environment. The oil-soaked sorbent in the mesh was
removed and drained for a minimum of 10 min. After the removal
of excess oil that had adhered to the surface of the sorbent and
that was not adsorbed or absorbed, the sample was transferred to a
weighing balance and the sample weight was recorded. The
experiment was performed in replicate 10 times, and the average
value was taken for calculating the sorption capacity. (A video file
describing the experimental procedure is provided in the
Supporting Information.) The crude oil sorption capacity was
calculated as shown in eq 1:
oil sorption capacity =
(Sst − S0)
S0
Brunauer−Emmett−Teller (BET) Surface Area Analysis.
Two cotton samples were characterized for their BET surface
area, using an automated gas sorption analyzer (QuadraSorb SI
Surface Area and Pore Size Analyzer, Quantachrome Instruments, Boynton Beach, FL). Our laboratory does not have this
instrument; therefore, we were limited, with regard to the
number of samples that could be tested. However, the two
samples tested represented a good range in their micronaire
value and, hence, were chosen for the BET testing. Tested samples
were outgassed at 120 °C for 3 h. Adsorption isotherms were
obtained using krypton at a temperature of 77.3 K. Literature
suggests that krypton is a better adsorbate for the BET
characterization of samples with low surface area (such as cotton)
and has been found to measure the correct surface area values.20
Environmental Scanning Electron Microscopy. A fieldemission environmental scanning electron microscopy (ESEM)
system (Hitachi, Model S-4800), in conjunction with the
cryogenic system (Gatan, Model Alto 2500), was used to image
the cotton samples with and without oil. The samples were
(1)
where S0 is the initial dry sorbent weight, Sst the weight of sorbent
with oil at the end of the sorption test, and the quantity (Sst − S0)
the net oil sorbed. (All weights are measured in grams.)
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Research Note
Figure 2. Crude oil sorption by raw cotton fibers. (a) Effect of micronaire on oil sorption capacity (g/g). (Cross bars represent standard error of
means, n = 10; the regions denoted by an asterisk (*) represent P < 0.05, and the region marked as “n.s.” denotes data that are not significant.) (b)
Oil sorption capacity of raw cotton fibers, relative to the fiber characteristics. (The smaller the fineness value (millitex), the finer the fiber and the
higher its oil sorption. Fiber with a fineness of 149 millitex has higher oil sorption capacity, versus 175 millitex fiber. Statistical analysis was performed
using one-way analysis of variance with Tukey post-test. Statistical significance in oil sorption is shown between low-micronaire cotton (Micronaire 3.1)
and other cottons (Micronaire 4.3−4.6). (Cross bars represent standard error of means, n = 10.) (c) ESEM micrograph of sorption of crude oil by raw
cotton fibers via interfiber capillary uptake. (d) ESEM image of crude oil absorbed within the fiber showing swelling of the cotton fiber.
coated with platinum/palladium at −130 °C, and ESEM images
of the coated sample were captured at −130 °C.
cotton fibers investigated. Figure 2a shows the oil sorption
capacity of raw cotton fibers for a range of micronaire values.
Low-micronaire cotton (Micronaire 3.1) showed a sorption
capacity of 35.83 g/g, which was significantly higher than the
sorption capacity of high-micronaire cotton (Micronaire 4.6), which
was 30.5 g/g. An inverse nonlinear relationship was found between
micronaire values and oil sorption capacity (see Figure 2a).
We propose a new hypothesis for the oil sorption, which takes
into account the absorption within the fiber as an important
phenomenon, in addition to adsorption and interfiber capillary
RESULTS AND DISCUSSION
To investigate the effect of the micronaire of raw cotton and to
correlate cotton fiber characteristics with the crude oil sorption
capacity, raw cottons over a range of micronaires were tested.
(Table 1 lists the micronaire values for the cotton samples that
have been tested.) Results show that the crude oil sorption
capacity of low-micronaire cotton is highest among the different
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dx.doi.org/10.1021/ie4005942 | Ind. Eng. Chem. Res. 2013, 52, 6277−6281
Industrial & Engineering Chemistry Research
Research Note
Table 1. Micronaire Values of Cottona
sample
Cotton
Cotton
Cotton
Cotton
Cotton
Cotton
micronaire
A
B
C
D
E
F
3.1
3.5
4.3
4.4
4.5
4.6
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Supplemental video: Real-time video showing the oil sorption
by raw cotton tested according to ASTM F726-06, Test
Method for Sorbent Performance of Adsorbents, is available as
Supporting Information. In this video, Accel nondetergent SAE
30 motor oil was used to demonstrate the method instead of
crude oil. The method used in evaluating the crude oil sorption
capacity of raw cotton is exactly the same as demonstrated in
the video with the change being only the type of oil. The use of
crude oil in this video was avoided for safety reasons. The
material is available free of charge via the Internet at http://
pubs.acs.org.
(0.031)
(0.012)
(0.021)
(0.012)
(0.015)
(0.016)
a
Values within parentheses indicate standard deviation. bFor the
micronaire measurement, the following was observed: one repeat per
sample and three samples per cotton type.
distribution.4,15 The oil sorption is basically the uptake of oil by
the cotton fiber matrix, which involves mechanisms such as
adsorption, absorption, and interfiber capillary uptake in the fiber
matrix. This hypothesis is supported by the ESEM analysis.
Figures 2c and 2d suggest that oil is not only adsorbed on the
external surface of the fiber, but also diffused through the fiber
matrix via interfiber capillary uptake (see Figure 2c). In addition,
because the fibers used are raw, it is well-understood that raw
fibers are naturally in twisted form, and once they absorb oil, they
swell and become rounded, as is evident from Figure 2d. Thus, the
high sorption capacity observed for low-micronaire cotton fibers is
due to adsorption, interfiber capillary sorption, and absorption
within the fiber, as substantiated by the ESEM images.
Furthermore, to comprehend the effect of fiber characteristics
such as immaturity and fineness on fiber surface area and oil
sorption, BET surface area analysis using krypton was performed.
BET surface area values computed using krypton adsorption
isotherms for Micronaire 3.1 and Micronaire 4.6 cottons were
determined to be 0.665 m2 g−1 and 0.400 m2 g−1, respectively.
Since low-micronaire cotton is an immature fiber, it is finer and
has a collapsed structure, resulting in a slightly enhanced BET
surface area, compared to that of high-micronaire cotton.
Enhanced fineness, increased surface area, and less cellulose
deposition due to immaturity in low-micronaire cotton result in
higher oil sorption. The smaller the fineness of the fiber and lower
its maturity (see Table 2), the higher is the oil sorption capacity, as
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Cotton
Cotton
Cotton
Cotton
Cotton
Cotton
A
B
C
D
E
F
fineness [millitex]b
149
154
167
168
173
175
(2)
(4.7)
(1.1)
(0.6)
(0.6)
(5.5)
*E-mail: s.ramkumar@ttu.edu.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The work was supported by the Texas State Support Program
of Cotton Incorporated (Grants Nos. TX 08-307 and TX 12119) and The CH Foundation, Lubbock, TX. We acknowledge
Kitten Land Company, TX for cotton samples, Dr. Eric Hequet
(Texas Tech University) for supporting the fiber characteristics
evaluation and Mr. Riaz Ahmad (Quantachrome Instruments)
for the BET testing.
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maturity ratio [%]
84
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89
AUTHOR INFORMATION
Corresponding Author
Table 2. Properties of Cottona
sample
ASSOCIATED CONTENT
S Supporting Information
*
b
(1.2)
(2.1)
(1.2)
(0.6)
(0.6)
(2.5)
a
Values within parentheses indicate the standard deviation. For the
fineness and maturity ratio, the following was observed: one repeat per
sample and three samples per cotton type. bThe lower the millitex
value, the finer the fiber.
shown in Figure 2b. Results indicate that, in low-micronaire
cottons, the combination of higher surface area and increased
fineness leads to more sites for surface adsorption and interfiber
capillary sorption, which, in turn, results in higher absorption of oil
within the fiber than the coarser and more-mature high-micronaire
cotton fibers. In addition, swelling of the fiber due to oil
absorption within the fiber was also evident, in the case of raw
cotton fibers.
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Industrial & Engineering Chemistry Research
Research Note
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