Angewandte
Communications
Chemie
Gelation of Crude Oil
Rapid Room-Temperature Gelation of Crude Oils by a Wetted Powder
Gelator
Changliang Ren, Jie Shen, Feng Chen, and Huaqiang Zeng*
Abstract: Phase-selective organogelators (PSOGs) not only
exhibit ability to phase-selectively congeal oil from oily water
but also allow easy separation of gelled oil from the body of
water. However, all hitherto reported PSOGs either necessitate
carrier solvents for their dissolution or suffer from an
extremely slow action in gelling oil in the powder form. A
previously unexplored generally applicable wetting strategy is
now described to dramatically enhance, by up to two orders of
magnitude, gelling speed of the resultant wet but non-sticky
gelator in the powder form in crude oils of widely ranging
viscosities. Such unprecedented rapid gelling speeds enable
rapid gelation of six types of (un)weathered crude oils within
minutes at room temperature, making PSOGs one step closer
to their eventual practical uses as one of important oil spill
control technologies.
concerns logistical and technical deployment of volatile and
flammable carrier solvents especially on large scale.
As to powder gelators that can gel oil in the powder form,
[
3n]
all three known powder gelators reported by Sureshan and
[3o]
us suffer from an extremely slow action in oil gelation as
a result of their slow dissolution/diffusion speed in oil in the
powder form, and complete gelation of light crude oils takes
days under constant stirring. These slow gelling actions make
on-site collection of treated oil in ocean impossible, increase
the risk of oil pollution during and after gelation, and further
suggest inability of powder gelators to quickly solidify heavy
crude oil of higher viscosities.
At the present time, powder gelators able to solidify
a single type of light crude oil, not to mention heavy crude
oils, into stiff solid within minutes at room temperature still
remain unknown. This dilemma, however, is totally expected
and in line with our belief that discovering a powder gelator
for rapid gelation of crude oils at room temperature is an
almost insurmountable, if not impossible, task. This is because
the most striking characteristic of gelators is their inherent
ability to form an insoluble 3D-entangled porous network
capable of immobilizing the solvent molecules by surface
tension and capillary forces to produce non-fluidic solid-like
gels. In other words, fast dissolution of powder gelators into
a solvent to be gelled fundamentally contradicts with gelatorsꢀ
precipitation tendency in the same solvent, and slow gelling
action by powder gelators is thus very much anticipated.
Herein, we nevertheless succeeded in solving this appar-
ent paradox, and demonstrate here a general wetting strategy
that could dramatically enhance, by up to two orders of
magnitude, the dissolution and gelling speed of the gelator in
crude oil without compromising its oil-gelling ability. With
room-temperature operations, the resultant wet but non-
sticky gelator in the powder form exhibits unprecedented
ability to rapidly congeal six types of weathered and
unweathered crude oils of widely ranging viscosities within
minutes.
E
fficient and cost-effective separation of spilled oil from
water body on large scale represents an unsolved challenge to
environmental scientists and engineers. While the commonly
used clean-up techniques (for example, in situ burning,
[
1a]
[1b]
[1c–f]
skimmers, booms, solidifiers and sorbents
) to sepa-
rate oil from water are not very effective even when applied in
combination, other oil-controlling techniques, which rely on
[
1g]
[1h]
oil-scavenging bacteria or dispersants, do not remove oil
[
1i]
from water with oil-caused pollutions remaining in water
for long periods of time.
A recently emerged strategy toward alleviating or possi-
bly solving the challenge explores the use of phase-selective
organogelators (PSOGs) capable of selectively congealing oil
into floating gels in the presence of water for easy collection
[
2,3]
and reclamation of treated oil.
The existing PSOGs fall
within two categories: solution-based gelators and powder
gelators. For solution-based gelators, non-water oil-miscible
carrier solvent(s) is required for dissolution of the gelators,
followed by adding this gelator-containing solution into oily
water for phase-selective gelation of oil. Gelators of this
category are faced with at least two major challenges. One
involves high solubility of gelators in environmentally benign
solvents (for example, ethanol and ethyl acetate) that are
thousands of times less toxic than crude oil: except for our
Our recently reported Fmoc-based powder gelators (F-
Leu-C6 and F-Leu-C8; Figure 1a) were derived from a robust
yet modularly tunable monopeptide scaffold capable of
forming reliable gelling networks via the directional H-
bonding forces and strong aromatic p–p stacking forces
[
3o,p]
recently reported highly soluble gelators,
all hitherto
developed gelators necessitate the use of toxic or hot carrier
[
3e–m]
[3o]
solvents or a large amount of carrier solvents.
The other
arising from Fmoc groups (Figure 1b,c). These two gela-
tors, however, are very sluggish in gelation and could fully gel
only Grissik, an extra-light crude oil, after 24 and 46 h under
constant stirring with a loading amount of 6% w/v (for
example, 6 mg per 100 mL of oil), respectively. Even at 20%
w/v and after three days, they still couldnꢀt solidify both light
[
*] Dr. C. L. Ren, Dr. J. Shen, Dr. F. Chen, Dr. H. Q. Zeng
Institute of Bioengineering and Nanotechnology
31 Biopolis Way, The Nanos, Singapore 138669 (Singapore)
E-mail: hqzeng@ibn.a-star.edu.sg
(
for example, Arab Light) and heavy (for example, Arab
Heavy and Ratawi) crude oils. In our quest to finding powder
Angew. Chem. Int. Ed. 2017, 56, 1 – 6
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!