NZ616152B2 - Oil absorbent composition - Google Patents
Oil absorbent composition Download PDFInfo
- Publication number
- NZ616152B2 NZ616152B2 NZ616152A NZ61615212A NZ616152B2 NZ 616152 B2 NZ616152 B2 NZ 616152B2 NZ 616152 A NZ616152 A NZ 616152A NZ 61615212 A NZ61615212 A NZ 61615212A NZ 616152 B2 NZ616152 B2 NZ 616152B2
- Authority
- NZ
- New Zealand
- Prior art keywords
- oil
- composition
- water
- charcoal
- absorbent composition
- Prior art date
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
- B01D17/02—Separation of non-miscible liquids
- B01D17/0202—Separation of non-miscible liquids by ab- or adsorption
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01J20/0225—Compounds of Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt
- B01J20/0229—Compounds of Fe
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- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
- C10B53/00—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form
- C10B53/02—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form of cellulose-containing material
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- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
- C12N1/00—Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
- C12N1/20—Bacteria; Culture media therefor
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- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
- C12N1/00—Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
- C12N1/26—Processes using, or culture media containing, hydrocarbons
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- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
- C12N11/00—Carrier-bound or immobilised enzymes; Carrier-bound or immobilised microbial cells; Preparation thereof
- C12N11/02—Enzymes or microbial cells immobilised on or in an organic carrier
- C12N11/10—Enzymes or microbial cells immobilised on or in an organic carrier the carrier being a carbohydrate
- C12N11/12—Cellulose or derivatives thereof
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E50/00—Technologies for the production of fuel of non-fossil origin
- Y02E50/10—Biofuels, e.g. bio-diesel
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/40—Bio-organic fraction processing; Production of fertilisers from the organic fraction of waste or refuse
Abstract
Disclosed herein is a method of preparing an oil absorbent composition. The method comprises heating and then de-mineralising a precursor plant material under conditions suitable to produce an oil absorbent composition comprising charcoal. The disclosure extends to oil absorbent compositions per se, such as charcoal-based compositions, and to various uses of the compositions for efficiently and rapidly absorbing spilled oil, for example from water surfaces, or from bituminous sands. such as charcoal-based compositions, and to various uses of the compositions for efficiently and rapidly absorbing spilled oil, for example from water surfaces, or from bituminous sands.
Description
OIL ABSORBENT COMPOSITION
The present invention relates to oil absorbent compositions, such as charcoal-based
compositions, and to methods of making such oil absorbent materials. The invention
extends to various uses of the compositions for efficiently and rapidly absorbing spilled
oil, for example from water surfaces, or from bituminous sands.
Oceans, soils, beaches, sea-bed sands and estuarine muds are commonly impacted by
oil spills causing significant environmental problems. Oil spill disaster responses
generally consist of three main measures, including containment of the spill using
booms, oil dilution and dispersion, and/or oil removal and recovery. It is estimated that
conventional methods of oil recovery, such as physical methods, including the use of
skimmers and pumping to recover the oil after an accidental spill, rarely recover more
than 10-15% of the spilled oil. Therefore, the second line of defence is the use of
dispersants or emulsifiers to break up the oil into small droplets that become dispersed
within the water. However, the use of dispersants and emulsifiers for the clean-up of oil
spills has been widely criticised because such substances are themselves often toxic to
aquatic life, and in some cases even carcinogenic, further exacerbating the toxicity of
the oil.
Although feathers, wool and peat have been suggested as oil absorbents, their large-
scale use is either impractical, or environmentally unsustainable in the case of peat.
The use of absorbents to ‘mop up’ oil spills is therefore unusual and the only
commercially available product on the market for this purpose is a product called ‘Sea-
sweep’, and is described in US 5,110,785. ‘Sea-sweep’ is produced from pine wood
(Pinus spp.) and is claimed to be able to absorb 3.5 times its own weight in oil. The
products’ effectiveness is claimed to be due to its hydrophobic nature and its tubular
internal structure. The tubular structure of the wood derived material is the result of
the xylem channels in wood. Hydrophobicity is imparted via heating the wood at
relatively low temperatures, i.e. no more than 380ºC. However, a significant problem
with this process is that, at such low temperatures, the wood from which these products
are derived degrades partly into hydrophobic molecules, i.e. creosotes that consist of
more than 90% poly-aromatic hydrocarbons (PAHs). Hence, although these molecules
are hydrophobic, they are also toxic.
US 4,605,640, on the other hand, describes the use of cellulose-containing substrates
that are impregnated with fatty quarternary ammonium salts, such as hexadecyl-
trimethyl ammonium bromide to make the materials hydrophobic. However, these
materials are not heated during their preparation, and their oil absorption capabilities
are comparatively poor.
Bituminous sands, also known as oil sands or tar sands, are a type of petroleum
deposit. The sands contain naturally occurring mixtures of sand, clay, water, and a
dense and extremely viscous form of petroleum, technically referred to as bitumen (or
colloquially “tar” due to its similar appearance, odour and colour). Oil sands are found
in large amounts in many countries throughout the world, but are found in extremely
large quantities in Canada and Venezuela. Because extra-heavy oil and bitumen flow
very slowly, if at all, towards producing wells under normal reservoir conditions, the
sands must be extracted by strip mining or the oil made to flow into wells by in situ
techniques, which reduce the viscosity by injecting steam, solvents, and/or hot air into
the sands. Most commonly, the oil is extracted using hot water and dispersants that
allows separation of the bitumen from the sand and clay. As a rule, around four barrels
of water are used to extract one barrel of bitumen. This process therefore generates
vast quantities of processed water that is contaminated with oil. This water has to be
stored in lagoons, known as ‘tailing ponds’. There is therefore a need for the water in
these tailing ponds to be cleaned up and for the remaining oil to be extracted. It is an
object of the present invention to go some way to meeting this need; and/or to at least
provide the public with a useful choice.
The inventors focused their research on a wide variety of plant-derived, cellulosic
materials, and have devised a more efficient method for preparing an oil absorbent
composition, which exhibits superior oil absorbent properties compared to products
currently on the market.
According to a first aspect of the invention, there is provided a method of preparing an
oil absorbent composition, the method comprising heating and then de-mineralising a
precursor plant material under conditions suitable to produce an oil absorbent
composition comprising charcoal, wherein the charcoal comprises non-activated
charcoal.
Surprisingly, the inventors observed that the method of the invention produces a
charcoal composition, which exhibits extraordinarily high oil absorption capabilities.
Indeed, as described in the Examples, and with reference to Figures 3-6, the inventors
have observed that when contacted with oil, the absorbent composition that is
produced by the method soaks up the oil within a matter of only seconds and the
resultant oil/composition forms aggregates that float on the water surface. This
prevents the oil from forming a thin oil film on the water surface. Instead, the
aggregates can be easily removed from the water surface using conventional oil
recovery methods such as skimmers, and booms. For example, when spread on top of
an oil spill on water, the composition of the invention has been shown to absorb about
-10 times its own weight in oil. This extraordinary ability to absorb oil to such an
extent is achieved by using a demineralised charcoal that is derived from a plant
material that preferably contains a high concentration of cellulose, but little or no
lignin.
Whereas the thus created composition of the invention is exceptionally effective at
absorbing oil when contacted with an oil spill, the composition can absorb water if
contacted with water before being contacted with oil, making it less suitable as a barrier
material for preventing the further spread of an oil spill. Furthermore, dispersed oil is
not absorbed as efficiently either, because water that is taken up in the process can
prevent oil absorption. In order to overcome this problem, the inventors have devised a
treatment process that involves contacting the oil absorbent composition (once formed)
with a water repellent substance.
Thus, the method may comprise contacting the oil absorbent composition with a water
repellent substance. The water repellent substance may comprise lipid. For example,
the repellent may be selected from the group consisting of: a fat; animal fat; plant fat; a
fatty acid; a fatty acid ester; a fatty alcohol; a glyceride (mono-, di- or tri-glyceride); a
hydrocarbon, such as a paraffin wax or tar; and mineral tar. One example of a plant fat
is coconut butter. In embodiments where the composition is used to absorb (crude) oil,
and if it were subsequently heated to desorb the volatile fractions, the non-volatile
fractions (i.e. tars) would remain within the char, making the material highly
hydrophobic and suitable for further use as an oil absorbent product.
Preferably, the water repellent substance may be paraffin wax, because of its
availability, ease of application and non-toxicity. This wax is solid at room temperature,
has a melting point of 56 C, and is a gas above 150 C. The oil absorbent composition (or
char) may be impregnated with the water repellent substance, such as paraffin wax.
During this process, the composition is contacted with hot paraffin gas that is sorbed
therein allowing it to form a thin coating onto exposed charcoal surfaces. Once cooled,
the paraffin solidifies and does not leach from the char.
Accordingly, the water repellent substance may be contacted with the oil absorbent
composition such that it is adsorbed into the micropores and/or mesopores of the
absorbent composition. The water repellent substance may be in a gaseous form when
it is contacted with the oil absorbent composition.
Whereas this process reduces the absorbing capacity of the material slightly, depending
on how much water repellent substance is allowed to sorb, it has the considerable
advantage that the resultant composition is now extremely hydrophobic so that it does
not take up water. This means that it can be contacted with water before being
contacted with oil without negatively affecting the oil absorption characteristics (see the
results in Tables 5 and 6), making it eminently suitable to be used to absorb dispersed
oil (see Figure 7).
The oil absorbent composition formed by the above methods can be referred to as
biochar. Once contacted with oil, the charcoal product forms oil containing aggregates
that contain little or no water, and can therefore be easily recovered from the water
using a sieve, suction sweeper or a fine-meshed net. Furthermore, since the
composition does not take up significant amounts of water when applied to an oil spill,
it allows efficient recovery of oil from water surfaces. In addition, because the
composition is inert and consists of >90% of carbon (i.e. charcoal), it does not alter the
properties of the absorbed oil. Accordingly, as described in the Examples, another
advantage of the invention is that it is possible to readily recover the absorbed oil from
the absorbent composition, which can be subsequently re-used.
The inventors have tested a wide variety of precursor plant materials, and have found
that certain species of plants (i.e. both wood-derived and non-wood-derived) provide
suitable precursor materials for use in the method of the first aspect, and can therefore
be used to produce the highly efficacious charcoal-based oil absorbent. Preferably, the
precursor material has a high cellulose content. The preferred source materials from
which the composition is derived contain in general no lignin and the carbon fraction of
these materials consists normally entirely of cellulose and hemi-cellulose.
Whereas source materials comprising mainly cellulose are preferred, low density woody
materials that contain lignin will, when charred in the method of the invention, also
make a good oil absorbent. Thus, in one embodiment, the precursor material may
comprise, or be derived from, any woody plant material. For example, the precursor
material may comprise, or be derived from, any hardwood species of plant, such as
paulownia (Paulowniaceae spp.), aspen (Populus tremulis) and other poplar species
such as cotton wood (Populus deltoides), balsa wood (Ochroma pyramidalis),
butterwood (Platanus occidentalis), walnut (Juglans regia) or willow (Salex spp.).
These species have typical wood densities of <500 kg m . Thus, it is preferred that the
wood used to make the char has a low density.
Alternatively, the precursor material may comprise or be derived from a softwood
species, preferably a low density softwood, for example a conifer (Picea spp.), pine
(Pinaceae spp.) or cedar (Cedres spp.). The inventors were surprised to observe that
char produced from paper and cardboard that were derived from wood pulp from
which most if not all of the lignin had been removed displayed excellent oil absorption
characteristics. Paper pulp can be derived from any wood, and is independent of its
density. Accordingly, in one embodiment, the precursor material may be paper or
cardboard, which may be contacted with a suitable binder such that it forms papier-
mâché. A suitable binder may be carboxyl methyl cellulose. It will be appreciated that
papier-mâché can be readily shaped into particles, such as granules, balls, pellets,
sheets, etc. When the papier-mâché is subsequently heated in the method of the
invention, the charred product still retains its shape, but becomes exceptionally
absorbent, producing a material that is capable of absorbing over nine times its own
weight in oil (see Table 2 in the results section).
In another embodiment, however, the precursor material may comprise non-woody
plant material, or is derived from any non-woody plant species. Examples of non-
woody plant materials, which may be used in the method, include those that are
derived from a plant family selected from the group of families consisting of
Brassicaceae, Poaceae, Amaranthaceae and Urticaceae. Examples of non-woody plant
materials may include those derived from a genus selected from Brassica or Hordeum.
Suitable species of non-woody plant material may include Brassica napus (oilseed
rape), Hordeum vulgare (Barley), Triticum aestivum (Wheat), Secale cereale (Rye)
Myscanthus (Elephant grass) or Zea mays (Maize).
Suitable precursor materials used in the method may be derived from any part of a
plant, for example the trunk (i.e. inner core wood, sap wood or outer bark), a stem (i.e.
inner or outer sections, or straw), the branches (inner or outer sections), a root (i.e.
inner or outer sections), or a leaf, depending on whether it is derived from a hardwood,
softwood or non-woody plant source. Preferably, the precursor material forming the
absorbent composition comprises, or is derived from the stems of non-woody plants.
The materials preferably contain mainly cellulose and hemi-cellulose.
The precursor material may be heated in the method of the first aspect to a temperature
greater than 280°C, 300°C, 325°C, 350°C, 375°C, 400°C, 425°C, 450°C, 475°C, 500°C,
o o o o
600 C, 700 C, 800°C, 900 C, or even greater than 1000 C. Pyrolysis temperatures
greater than 800 C are possible, but may lead to increasing amounts of carbon loss.
Whereas carbon loss equates to a loss in product yield, a subsequent demineralisation
step would restore any reduction in absorption capacity. The precursor material may
be heated for a sufficient period of time for pyrolysis to be completed to produce the oil
absorbent composition.. For example, heating may be for a very brief period when
using flash pyrolysis, for example a heating time of less than 1 minute. However, long
heating times are possible, such as at least 10 minutes, at least 20 minutes, at least 30
minutes, at least 40 minutes, or at least 60 minutes. The material may be heated for at
least 70 minutes, at least 80 minutes, at least 100 minutes, at least 110 minutes, or at
least 120 minutes. In some embodiments, the material may be heated for more than 2
hours, such as 3, 4, 5 or even 6 hours or more. However, it should be understood that
prolonged heating times are normally not necessary as long as all the material exposed
to the heat is pyrolysed during the process. The length of time that the precursor
material needs to be heated is dependent on how the material is presented (loose or
baled for example) and the heating temperature. The greater the mass and the greater
the density, the longer the material needs to be heated to allow the heat to penetrate
and cause pyrolysis. Fine particles that are heated at a high temperature on the other
hand will be charred within seconds.
As described in the examples, charring at about 450°C until complete pyrolysis was
achieved was found to be particularly effective. Accordingly, the precursor material may
be heated at a temperature of between about 280°C and about 1200°C, or between
about 350°C and about 800°C, or between about 400°C and about 600°C. Preferably,
the precursor material is heated under substantially anaerobic conditions.
The inventors were surprised to find that the de-mineralisation step carried out in the
method of the first aspect resulted in a significant increase in oil absorption (i.e. by an
astounding 50% for nettle straw) compared to when the precursor material was not
demineralised. Not only does the demineralisation step result in an open porous
structure within the charcoal into which oil may be absorbed, it also results in an
absorbent composition which is much less dense than prior to the demineralisation
step, and this reduction in density is believed to be particularly advantageous in
treating oil spills, because the resultant composition floats on the treated water for
longer periods of time, a characteristic that can be further enhanced by treating the
composition with a water repellent substance, such as a lipid, or with for example
paraffin wax. Accordingly, much more oil is absorbed by the absorbent composition
than would be the case if the composition sank in the water, away from the oil floating
on the surface. Furthermore, advantageously, the absorbent composition allows the
recovery of valuable (i.e. useful) plant minerals during its production because of the de-
mineralisation step.
The demineralisation step in the method may be achieved by contacting the precursor
material with an acid, preferably following the heating step, for a suitable time period
to allow for the removal of mineral ions from the previously heated precursor material.
The acid may be any acid or a combination of acids, but sulphuric acid, hydrochloric
acid or nitric acid, are all suitable. The pH of the solution should preferably be less than
4.0, more preferably less than 3.0, or preferably less than 2.0, and even more
preferably less than 1.0. The lower the pH, the faster the demineralisation occurs and
the less chance the minerals react with the acid, causing a significant pH rise of the
solution. A strong acid is preferred. For example, nitric acid, in particular, is
advantageous, because it allows the harvesting of valuable fertilisers from the heated
material in the form of potassium nitrate, calcium nitrate and/or magnesium nitrate.
The heat-treated precursor material may be contacted with the acid for several hours,
and preferably at least 12, 24, 36 or 48 hours or more, depending on the acid strength,
and the particle size of the char with longer contact times being necessary to dissolve
the minerals if the char particles are larger. The acid wash treatment solubilises and
removes the minerals within the pore structure of the precursor material, leaving
behind an open porous structure, which lowers its density.
Removal of some elements (potassium, for example) from the oil absorbent
composition can also be achieved by contacting the composition with a buffered
solution having a neutral or a slightly acidic pH. Depending on the precursor material
from which the absorbent composition is derived, this can lead to the removal of >50%
of all the minerals therefrom. In many cases, (slightly) acidic buffers will be capable of
removing all minerals from the absorbent composition.
Hence, in contrast to current materials that are used as oil absorbents, which have high
mineral contents, the absorbent composition produced by the method of invention has
a much lower mineral content because of the demineralisation step. The term “low
mineral content” can refer to the concentration of elements or metal ions contained
within the absorbent composition. For example, the composition may comprise a low
concentration of alkali and/or alkaline earth metals. The concentration of alkali and/or
alkali earth metals in the absorbent composition may be less than 3% (w/w), less than
2% (w/w), less than 1% (w/w), less than 0.5% or less than 0.1% of dried material.
Drying may be carried out by warming at 100ºC for 28 hours, for example. Examples of
alkali metal and alkaline earth metals may include potassium, calcium, sodium and/or
magnesium.
Thus, the absorbent composition may have less than 2% (w/w), less than 1% (w/w) or
less than 0.5% (w/w) potassium or potassium ions of dried material.
The absorbent composition may have less than 2% (w/w), less than 1% (w/w) or less
than 0.5% (w/w) magnesium or magnesium ions of dried material.
The absorbent composition may have less than 2% (w/w), less than 1% (w/w) or less
than 0.5% (w/w) calcium or calcium ions of dried material.
The absorbent composition may have less than 2% (w/w), less than 1% (w/w) or less
than 0.5% (w/w) sodium or sodium ions of dried material.
The absorbent composition may comprise any combination of any of the foregoing
elements (i.e. minerals) at any of the above-mentioned concentrations. Thus, the total
concentration of potassium, magnesium, calcium and/or sodium may be less than 5%
(w/w), less than 2.5% (w/w) or less than 1% (w/w) of dried material.
After the demineralisation step, the method may then comprise a step of separating the
resultant absorbent composition from the acid, for example by filtration or
centrifugation. Following separation from the acid, the method may further comprise
adjusting the pH of the composition until the pH indicates that the majority of the acid
has been substantially neutralised. This pH adjustment may be achieved, for example,
by washing with water, or addition of a base. Slight acidity at this stage may be the
result of carboxyl groups formed on the composition’s surface during exposure to the
acid during the acid wash. Once washed, the method may then comprise a drying step
to provide the absorbent composition, which is then ready for use, as a product that can
be applied directly onto an oil spill. However, a further treatment step where the
composition is contacted with a water repellent substance (e.g. paraffin, wax, tar, fat
etc.) may also be carried out.
According to a second aspect of the invention, there is provided a composition, suitable
for absorbing oil, obtained from the method according to the first aspect.
Figure 1 shows that the lower the density of the absorbent material, the greater it’s oil
absorbing properties. Thus, the density of the absorbent composition may be less than
0.2 kg/L, 0.17 kg/L, 0.15kg/L or less than 0.14kg/L.
In a third aspect, there is provided a composition, suitable for absorbing oil, comprising
charred charcoal comprising, or being derived from, plant material, wherein the
charcoal has a density less than 0.2kg/L and a mineral content of less than 10% of dried
material and the charcoal comprises non-activated carbon.
The composition of the third aspect may also be obtainable by the method of the first
aspect. The density of the absorbent composition of the third aspect may be less than
0.17 kg/L, 0.15kg/L or less than 0.14kg/L. The mineral content of the composition of
the third aspect may be less than 10% alkali metal and alkaline earth metals, which may
include potassium, calcium, sodium and/or magnesium.
Unlike prior art oil absorbent materials, there is no need for the compositions of the
invention to have an internal network of tubes and capillaries. Instead, it is sufficient if
the absorbent composition comprises a random, loosely arranged structure that
contains voids into which oil can be absorbed. Indeed, the absorbent composition may
be substantially macroporous. Pores in a sorbent derived from wood are called
“macropores” if their pore size is greater than 500nm in diameter. For practical
purposes, pores having diameters in the range of 500nm to 40,000nm, more typically
500 to 20,000nm, or 500 to 15,000nm, may be classified as macropores.
Although not wishing to be bound by theory, the inventors believe that macropores are
an example of voids that are present in the absorbent composition derived from wood,
but that non-tubular, continuous and interconnecting voids that are present in charred
papier-mâché, for example, are just as effective at absorbing oil as macro-pores. In
fact, the inventors have surprisingly found that destruction of pores and voids by
grinding the absorbent composition into a fine powder of less than 60 µm in diameter
had no significant effect on the charcoal’s ability to absorb oil (see examples, Table 1).
This shows that, unlike what is claimed in the prior art, absorption is not governed by
capillary action of an intact and continuous tubular structure, as found in charred
wood. Once the composition of the invention is contacted with oil, the oil will cling to
the available charcoal surfaces and form a film around them. Particles will subsequently
attract each other forming a raft or aggregate that can be easily recovered. This means
that more oil can be removed from the environment. This is because the absorbed oil in
the composition is lighter than water resulting in the product and absorbed oil floating
on the water surface where it can be easily removed. Because the composition does not
react with the absorbed oil, the absorbed oil can be easily recovered , for example via
centrifugation or by desorbing (e.g. volatilising) the oil by applying heat to the ‘spent’
product that volatiles the absorbed oils and greases Finally, the spent product can be
directly used as a fuel.
The absorbent composition may take on the form of a fine powder or small lumps. In
general, small particles absorb oil more rapidly than larger ones, but large particles will
float for longer periods of time because the air trapped inside them allows them to stay
buoyant for longer. Whereas this seems an advantage, the effectiveness of the
composition to absorb oil decreases rapidly once water is absorbed. In embodiments
where the composition has not been treated with a water repellent substance, it is
important that the composition is directly applied to an oil spill to prevent absorption
of water before the oil is contacted by the composition.
The mean particle size of the absorbent composition may therefore be of any size, but a
particle size between 0.01mm and 50mm, or between about 0.01mm and 25mm, or
between about 0.1mm and 10mm, or between 0.1mm and 5mm, or between 0.1mm and
1mm is effective. In one embodiment, the mean particle size may be less than 2mm, or
less than 1mm, or less of than 0.5mm, or less than 0.1mm, or less than 0.01mm. In
another embodiment, the mean particle size of the absorbent composition may be
greater than 2mm, 3mm, 4mm, or greater than 5mm. Larger particles are easier to
handle and can be dropped onto an oil spill much easier than small particles which can
easily blow away before they reach the spill. Furthermore, finely powdered charcoal
can present an explosion hazard when stored in a closed environment. Therefore, it is
preferred that the particles are greater than at least 1mm.
To prevent formation of charcoal dust that can be easily blown away, in a further
aspect, it is preferred that the compositions of the second and third aspects of the
invention may be treated with a small quantity of oil, for example up to 10% of the
biochar weight. Thus, the composition may comprise up to 10% (w/w) oil. Oil used for
this purpose may be mineral oil or vegetable oil.
To prevent the composition taking up water, in a further embodiment the composition
may be treated with a water repellent substance. This may involve contacting the char
with hot paraffin gas, melted fat or heating of char that has been allowed to absorb oil
to remove any liquid or volatile fractions. Thus, the oil absorbent composition may
comprise a water repellent substance. The water repellent substance may comprise
lipid. For example, the repellent may be selected from the group consisting of: a fat;
animal fat; plant fat; a fatty acid; a fatty acid ester; a fatty alcohol; a glyceride (mono-,
di- or tri-glyceride); a hydrocarbon, such as a paraffin wax or tar; and mineral tar.
In another embodiment, the absorbent composition may comprise a mixture of
differently sized particles. For example, the inventors have found that a mixture of
absorbent particles less than about 0.5 mm and particles larger than about 5mm
surprisingly results in the particles sticking together in large rafts making it easy to
remove the absorbed oil using nets or booms. Therefore, the composition may comprise
a mixture of absorbent particles having a mean particle size of between about 0.01 and
0.5mm (i.e. small particles) and between about 5mm and 100mm (i.e. large particles).
The ratio of smaller to larger particles sizes may be between 1:10 and 10:1, or between
1:5 and 5:1, or between 1:3 and 3:1, and most suitably between 1:2 and 2:1. The ratio of
smaller to larger particles sizes is preferably about 1:1. An added advantage of using a
mixture of particle sizes is that the larger particles will stay afloat longer than the
smaller ones, while the smaller particles (because of their relative large surface area)
will absorb the oil more readily.
In one embodiment, the absorbent composition may be magnetic, and so may
comprise, non-valent iron, iron oxide or iron hydroxide. It will be appreciated that the
resultant material will exhibit magnetic properties allowing it to be removed effectively
from oil/water mixtures using magnets. The skilled person will appreciate that there
are several methods by which iron-oxide/hydroxide may be incorporated into the
charcoal absorbent composition. For example, the charcoal may be contacted with, or
soaked in, a solution containing FeSO .7H O. Once soaked into the charcoal, the
charcoal may then be removed from the solution and dried. Subsequently, the charcoal
may be contacted with a solution of NaOH (e.g. 1M), which will cause the sulphate ions
to be replaced by hydroxide ions. The amount of iron hydroxide within the biochar
composition can be increased by soaking the charcoal in a more concentrated solution
of FeSO .7H O. Clearly, incorporation of iron (oxide/hydroxide) into the composition
will increase the mineral content of the composition. Preferably, the iron oxide or iron
hydroxide is incorporated to a level where it does not cause the absorbent particle to
become so heavy that it sinks. This feature would make it ideal for the removal of oil,
for example from oil-contaminated water (e.g. bilge water), by first contacting the
composition with the contaminated water allowing it to absorb the oil, and then passing
the water past a strong (e.g. electro-) magnet to which the absorbent composition, and
absorbed oil, will be attracted. This feature would prevent clogging of sieves or filters
designed to remove oil or particles.
Advantageously, the absorbent composition enhances the degradation of an oil slick by
allowing oxygen to penetrate into the oil slick, as the product works like a bulking
agent. Hence, in another embodiment, the absorbent composition may comprise an
oxygen-releasing agent, such as magnesium peroxide or calcium peroxide. This can be
achieved by mixing the composition simply with a peroxide powder which would be
applied together onto an oil spill. As the charcoal binds the oil together in aggregates,
the peroxide is incorporated into the mixture. As the peroxide releases oxygen, it helps
to enhance aeration, and therefore natural attenuation, of the oil.
In a further embodiment, the absorbent composition may be mixed with slow release
fertilisers that contain nitrogen (ammonium nitrate for example), phosphate, or
potassium, and/or a selection of micro-nutrients, such as Fe, Cu, Co and Zn, as well as
vitamins to enhance the growth of hydrocarbon-degrading microorganisms. The
charcoal composition will enhance the incorporation of these fertilisers into the oily
aggregates that are formed as a result of the addition of the charcoal to an oil spill. In
cases where the oil is not recovered from the water surface, these nutrients help to
overcome any shortages of minerals necessary for the degradation of the different
hydrocarbons that make up the oil.
In yet another embodiment, the absorbent composition may be inoculated with a
community of oil-degrading bacteria. For example, the bacteria may be isolated from a
marine environment that has been previously contaminated with oil. Suitable oil-
degrading bacteria may belong to genera such as Pseudomonas, Bacillus,
Staphylococcus, Acinetobacter, Kocuria and Micrococcus. The preferred microbial
genus may be Bacillus. Not only are there extremely effective hydrocarbon degraders
within this genus, but this genus produces endospores that resist desiccation and
extremes of temperatures. Therefore, adding the hydrocarbon-degrading microbes as
endospores will allow long-term survival of the preparation when the product is stored
and rapid establishment once the product is applied.
As described herein, the absorbent compositions of the invention can be applied in a
range of different scenarios for absorbing oil from water, e.g. oil slicks.
Thus, in a fourth aspect, there is provided use of the composition according to either
the second or third aspect, for absorbing oil.
The oil may be mixed with an oil-contaminated material, such as a fluid, or sand. The
oil in the contaminated material may be emulsified.
In a fifth aspect, there is provided a method for absorbing oil from an oil-contaminated
material, the method comprising contacting an oil-contaminated material with the oil
absorption composition according to either the second or third aspect, and allowing the
oil to be absorbed by the composition.
The oil-contaminated material may be a fluid, such as water. For example, the
composition may be spread or sprayed on top of an oil spill on water, which results in
the formation of oil/composition aggregates.
The oil-contaminated material may be oil-contaminated sand, bituminous sand or
process waters. Process waters contaminated with oil may be cleaned and dispersed oils
can be removed from suspension by contacting with the composition of the invention
especially in embodiments where the composition is made hydrophobic by contacting
with a water repellent substance.
The method may comprise a step of separating the oil absorption composition from the
oil-contaminated material. For example, the separation step may comprise use of a
sieve, suction sweeper, a fine-meshed net or a magnet, a mop consisting of ropes or any
other physical device designed to remove oil from a water surface. Alternatively, the
composition may be used as a filter material through which oil contaminated water is
passed.
The method may comprise a step of recovering the absorbed oil from the absorbent
composition. One method for recovering the oil from the composition would be to
process (i.e. refine) the adsorbed oil as if it were pure crude oil using distillation. In an
oil refinery, the composition and its absorbed oil would be heated and the different
fractions collected for further use. The charcoal being non-volatile would end up in the
tar fraction. Alternatively, an emulsifying agent may be added to release the oil from
the composition or the oil may be recovered using centrifugation.
All of the features described herein (including any accompanying claims, abstract and
drawings), and/or all of the steps of any method or process so disclosed, may be
combined with any of the above aspects in any combination, except combinations
where at least some of such features and/or steps are mutually exclusive.
For a better understanding of the invention, and to show how embodiments of the same
may be carried into effect, reference will now be made, by way of example, to the
accompanying diagrammatic drawings, in which:-
Figure 1 is a graph showing the correlation between charcoal density and oil uptake;
Figure 2 shows a SEM micrograph of the macropore structure of sweet chestnut
charcoal which has been charred at 450 C;
Figure 3 shows photographs of oil recovery using charred cellulose material. A: oil on
water, B: following treatment, C: treated water after being passed through a 500µm
sieve, D: oil/char residue on the 500µm sieve;
Figure 4 shows photographs of oil recovery using Treatment 7 vs Treatment 2.
E: Treatment 7 involves adding an emulsifier to sand and oil, followed by the addition
of water, and then charcoal. F: Treatment 2 involves adding charcoal after the
emulsifier has emulsified the oil out of the sand;
Figure 5 shows photographs of the recovery of oil from sands. G: Treatment 7-
Control; Sand, Oil, Water; H: Emulsifier added to G; I: Sweet Chestnut Charcoal added
to H; J: I left for 2 weeks;
Figure 6 shows photographs of a step-by-step process of the recovery of oil from sand.
K: Oil added to sand, and then water added; L: Emulsifier added to K (Note the oil
emulsifying into the water); M: Oil fully emulsified out of the sand into the water; N:
Sweet Chestnut charcoal added to M (Note oily aggregates floating on surface); and
Figure 7 shows removal of emulsified oil using a hydrophobic oil absorbent
composition which has been treated with paraffin.
Examples
Introduction
Charcoal is a porous material that is slightly hydrophobic. When derived from wood,
the structure of the charcoal reflects the macroporous structure of the wood from which
it is derived. Pyrolysis leads to around 70% mass loss of the wood and results in a
structure that is >90% void. However, macropores within the charcoal are lost when
the charcoal is ground up, leaving a carbon structure that consists mainly of meso- and
micro-pores. In non-activated carbons, the volume of meso- and micro-pores is
normally relatively small such that the solid fraction of pyrolysed wood consists mainly
of graphite-like materials.
Sea-sweep, which is described in US 5,110,785, is an oil-absorbing product derived
from torrified pine wood, and claims to rely mainly on the macroporous nature of the
material to absorb oil. Although not wishing to be bound by theory, the inventors
hypothesised that the macropores of wood are relatively unimportant for charcoal’s
ability to absorb oil, and instead it was hypothesized that the pyrolysed carbon itself is
responsible for absorbing oil by acting as a ‘binding agent’ that results in the formation
of oily aggregates. How effective different charcoals are at forming such aggregates was,
however, unknown.
A common method for treating oil spills is to apply dispersants or emulsifiers which
form macro- and micro-sized droplets of oil in suspension within waters. Such
emulsifiers have been shown in some cases to cause toxicity to aquatic life. The
inventors therefore believe that the charcoal-containing compositions of the invention
would absorb emulsified oil from waters. Furthermore, the inventors have
demonstrated that removal of the charcoal/emulsified oil is effective. There is also
potential for testing using standard eco-toxicity to demonstrate that the captured
emulsified oils are less environmentally damaging than their non-absorbed
counterparts.
Soils, beach and sea-bed sands and estuarine muds are commonly impacted by oil
spills, and washing or submersion within water does little to release the absorbed oil.
However, the application of a washing process with an appropriate emulsifier or a
dispersing agent can be used to release the soil/sand-absorbed oils into suspension
within water. The inventors have therefore tested the ability of the charcoal
compositions of the invention to remove oil in suspension within such material
washings.
Lastly, the inventors have also tested whether the charcoal-containing compositions of
the invention can be used with emulsifiers to remove oil from oil sands. Accordingly,
the inventors believe that the charcoal-oil mix can be pre-processed (i.e. upgraded) to a
refinery standard.
Materials and Methods
Importance of macropores for oil absorbance
To assess if macropore volume is a significant factor in oil uptake, the density of
charcoals derived from different wood species was assessed. A charring temperature of
450 C was used. The material was heated for approximately 2 hours to ensure
complete pyrolysis of the wood. First, a lump of charcoal was weighed, and it was then
soaked in oil to make the lump hydrophobic and incapable of soaking up water. Excess
oil was removed by washing the oil-soaked lump of charcoal under a tap of water. The
lump of charcoal was then attached to a needle and the volume of the lump was
measured using water displacement. To achieve this, a measuring cylinder was filled
with water and the oil-soaked lump of charcoal was pushed below the water surface,
and the increase in volume was recorded. Density was expressed as weight of charcoal
/ volume of charcoal. Oil absorbance was subsequently correlated with wood density.
It was expected that since most of the ‘void spaces’ are macropores, there would be a
strong correlation between wood density and oil absorbance.
To test if macropore structure of wood-derived charcoals was important for the
absorption of oil from a water surface, Paulownia wood that was charred at 450 C, was
ground with a pestle and mortar and passed over a nest of three sieves; 500µm, 150µm
and 60µm sieve to obtain four size classes of charcoal (<60µm, 60-150µm, 150-500µm
and >500µm). Grinding will destroy the macropore structure of a charcoal such that
the largest particles had an almost intact macropore structure, while the smallest size
class consisted mainly of charcoal charts with few intact pores.
To test the role of macropores for oil absorbance of the different charcoal particles, a
250 ml Duran bottle was filled with approximately 100 ml water. The bottle with water
was placed on a balance and tarred to zero. Subsequently, 1 g of oil was dropped onto
the water surface. Charcoal was added slowly on top of the oil with intermittent
swirling of the water to speed up the process of bringing the charcoal into contact with
the oil. This process was continued until all of the oil was absorbed from the surface of
the water. The minimum amount of charcoal needed to absorb all of the oil was
recorded. Treatments were replicated three times and the results were analysed using
ANOVA. Significant differences between treatments were assessed using Tukey’s test
for significant differences between pairs of treatments.
Effect of source material on absorbance of oil
Absorption of charcoals derived from eleven different source materials (Papier-mâché,
Mount-board, cellulose sponge, Barley Straw, Oil-Seed Rape straw, Ash Wood, Beech
Wood, Paulownia Wood, Sweet Chestnut Wood, Spruce Wood, Pine Wood, Cyprus
Wood, and Oak Wood) were tested. Furthermore, both the charcoals derived from
barley straw and oilseed rape straw were acid-washed in hydrochloric acid (pH < 1) to
remove the minerals that were associated with these chars. Hence, a total of 15
materials were tested for their ability to absorb oil using the method described above.
Recovery of oil from water
The ability to recover oil from water using the above method was tested by passing the
absorbed oil + water over a pre-weighted 500µm sieve, removing excess water using a
paper towel and then further air drying for an hour before weighing the sieve and the
charcoal/oil deposit. For experimental purposes, a 500 ml Duran bottle containing
200 ml water was amended with 3 g oil and 0.5 g product. Because the theoretical
weight of the combined oil and charcoal was known (3.5 g) and assuming that no oil
was left in the water (which was clear) an estimate could be made of how much water
was taken up by the charcoal. Only the best materials (demineralised barley straw,
demineralised oilseed rape straw and papier-mâché) were tested in triplicate.
Recovery of emulsified oil from water
The ability of 5 g charcoal product to remove emulsified oil from waters was tested. For
experimental purposes, a 500 ml beaker was used containing 250 ml water amended
with 5 g oil emulsified into suspension within the water with 5 g emulsifying agent
(Decon 90). A visual assessment of the absorption of the emulsified oils by the
charcoals was made. Both barley straw and sweet chestnut chars were tested in
triplicate to compare the effects of the different materials.
Recovery of oil from sands
The ability of charcoal to absorb oil, which had been brought into suspension using an
emulsifying agent so as to remove the oil from sand, was tested. For experimental
purposes, a 500 ml beaker was used containing 100 g sand (laboratory grade), two oil
treatments (5 g and 10 g), submerged in 200 ml water with 5 g emulsifying agent
(Decon 90) added (compared to control, zero g of emulsifying agent) and amended with
5 g and 10 g charcoal product. Both barley straw and sweet chestnut chars were tested
in triplicate to compare the effects of the different materials. Visual assessments of oil
absorption were made on the following treatments:
Emulsifier
Treatment Sand Crude Oil Water Charcoal
(Decon 90) Charcoal
No. /g /g /g /g
Sweet
1 100 10 200 5 10
Chestnut
Sweet
2 100 5 200 5 5
Chestnut
Barley
3 100 5 200 5 2
Straw
Sweet
4 (Control) 100 - 200 5 5
Chestnut
(Control) 100 5 200 - - -
6 (Control) 100 5 200 5 - -
A further treatment was tested (referred to here as Treatment No.7). The inventors
tested the ability of the emulsifying agent, when mixed directly with the oil impacted
sand, to suspend the oil when water was added. For experimental purposes, a 500 ml
beaker was used containing 100 g sand (laboratory grade), 5g of crude oil, with 5 g
emulsifying agent (Decon 90) submerged in 200 ml water and amended with 5 g of
sweet chestnut charcoal.
Biodegradation of captured oil within charcoal:
Here we left the oil impregnated charcoal (100 g sand, 10 g oil, 5 g emulsifying agent,
200 ml of water, 10 g sweet chestnut char treatment from Experiment 2.5) for 14 days
in a covered beaker (to prevent evaporative losses of volatiles) and conducted a visual
assessment of oil absorbed by the char.
Results
Importance of macropores for oil absorbance
Figure 1 shows that there is a weak negative correlation (r =0.790) between charcoal
density and oil uptake. However, there is a general trend that ‘low density’ chars are
better at taking up oil than ‘high density’ chars. None of the high density woods were
particularly absorbent. Whereas this indicates that macropore structure could play a
role in oil uptake, the inventors do not believe that it is the only factor.
Table 1: Effect of charcoal particle size on absorption of oil. Paulownia wood with size
classes of >500µm, between 500 and 150µm, 150 and 60µm and <60µm were used.
N=3.
Particle size (µm) Absorbance (ml/g)
> 500 4.58
150-500 4.44
60-150 4.39
<60 4.44
Significance Not significant
Table 1 shows that grinding the charcoal to particles <60µm had no significant effect on
the charcoal’s ability to take up oil, suggesting that the hydrophobic properties of the
charcoal itself were in the main responsible factor for oil absorbance and that
macropores were in the main not involved.
It could be argued that, because macropores in wood are normally around 10-15 µm in
diameter (see Figure 2), charcoal pieces with a diameter of <60µm could contain some
macropores. On the other hand, such pores would be very short, giving them next to no
capillary action.
Effect of source material on absorbance of oil
A variety of different source materials were tested for their oil absorbance capabilities.
Table 2: Oil absorbance of charcoals derived from different source materials. N=3
Source material Oil uptake (l kg ) SE
Cellulose materials
Barley Straw 7.97 0.328
Barley Straw 9.53 0.281
De-mineralised
Oilseed Rape Straw 5.35 0.329
Oilseed Rape Straw 7.81 0.467
De-mineralised
Papier-mâché 10.16 0.537
Cellulose sponge 9.25 0.000
Mount board 2.50 0.046
Lignin containing materials
(Soft woods)
Spruce 3.37 0.056
Pine 3.74 0.044
Cypress 3.09 0.089
Lignin containing materials
(Hard Woods)
Paulownia 4.44 0.089
Beech 3.39 0.100
Sweet Chestnut 1.96 0.056
Ash 1.99 0.056
Oak 1.29 0.022
P ***
Table 2 shows that there are large differences in the ability of different charred
materials to absorb oil, with charred papier-mâché capable of taking up >10 Litre oil
per kg material while charred oak wood was only capable of absorbing 1.3 Litre oil per
kg char.
De-mineralisation of chars derived from oilseed rape straw led to a 32% (P< 0.001)
increase in oil absorbance per unit weight and a 16% (P<0.05) increase in oil
absorbance for char derived from barley straw. This is almost exactly proportional to
the mineral contents of the source materials (mineral content barley char: 15% and
mineral content of oil seed rape char 30.3%).
Chars derived from materials with a high cellulose content (papier-mâché,
demineralised oilseed rape, cellulose sponge and demineralised barley straw) were on
average 3 times more effective at absorbing oil than chars derived from wood.
However, charred mount board was similar in its effectiveness of absorbing oil as
charred wood. Interestingly, the density of charred mount board was around 0.42g/ml
which is almost twice as dense as wood, while for example charred cellulose sponge had
a density of 0.13g/ml. Therefore, for a char to take up maximum amounts of oil, the
char needs to be arranged in a loose structure that provides a maximum amount of void
space, and most materials that are rich in cellulose seem to fit this characteristic.
Recovery of oil from waters
The inventors tested the efficacy for various oil absorbent materials to release absorbed
oil. Referring to Figure 3, there are shown photographs of oil recovery using charred
cellulose material. A: shows the oil dispersed on the water surface, and shows the water
following treatment with the composition of the invention. C shows the treated water
after being passed through a 500µm sieve, and D shows the oil/char residue on the
500µm sieve.
Table 3: Oil recovery using charred (and demineralised) barley straw and charred
papier-mâché. 0.5 g material was used to absorb 3 g oil
Source material Total weight Percentage SE
recovery
Demin Barley 3.45 99% 0.02
Papier-mâché 3.43 98% 0.03
significance NS NS
Table 3 shows that a large percentage of oil was recovered using charred and de-
mineralised barley straw or charred papier-mâché. Whereas it is possible that part of
the combined weight of the char and oil consisted of water, this is unlikely as there was
no visible oil left in the water, as shown in Figure 3. The small loss of oil and carbon can
be contributed to a small proportion of particles of char and oil passing through the
500 µm sieve. Assuming that the char and oil that was recovered on the sieve
contained no water, the method described here holds a lot of promise to recover oil
spills.
Recovery of emulsified oil from waters
A visual assessment of the treatments revealed that larger aggregates of charcoal (sweet
chestnut charcoal) floated in comparison to barley straw, whereas a larger proportion
of the charcoal sank. The sweet chestnut charcoal would therefore make for easier
recovery. The water became significantly clearer after addition of both of the charcoals.
The amount of absorbed oil seemed to be comparable in both charcoals, although the
higher mineral content of the barley charcoal made the water darker, therefore making
a visual comparison difficult.
Recovery of oil from sands
The inventors investigated the recovery of sand-absorbed oil. Referring to Figure 4,
there are shown photographs of oil recovery using Treatment 7 (i.e. E) vs Treatment 2
(i.e. F). Treatment 7, shown in Figure 4E, involves adding an emulsifier to sand and oil,
followed by the addition of water, and then charcoal. Treatment 2, shown in Figure 4F,
involves adding charcoal after the emulsifier has emulsified the oil out of the sand. As
can be seen, Treatment 2 (5g of sweet chestnut charcoal) was the most successful with
large oil aggregates floating on the surface. The water was transparent in comparison to
the control. Treatment 7 (Emulsifier added to sand and oil) was less successful and the
charcoal did not recover as much oil, and more oil remained in the water.
Referring to Figure 5, there are shown additional photographs of the recovery of oil
from sands. Treatment 7, i.e. sand, oil and water, is shown in Figure 5G, and acted as
the control. In Figure 5H, emulsifier was added to the mix shown in Figure 5G. In
Figure 5I, sweet chestnut charcoal added to the mix shown in Figure 5H. Finally, Figure
5J shows what happens to the mix shown in Figure 5I if left for 2 weeks to stand.
Referring to Figure 6, there are shown photographs of a step-by-step process of the
recovery of oil from sand. Figure 6K shows oil added to sand, and then water added.
Figure 6L shows the effect of adding emulsifier to the mix shown in Figure 6K. It
should be noted that the oil emulsifies into the water. Figure 6M shows oil fully
emulsified out of the sand into the water, and Figure 6N shows Sweet Chestnut
charcoal added to the mix shown in Figure 6M. It should be noted that oily aggregates
can be seen floating on the water’s surface.
The degradation of oil captured within the charred materials
Over a 2 week period, the water in Treatment 2 became much clearer and the charcoal
oily aggregates appeared to be separated from each other. When agitated, the oil was
not released back in to solution. The oil was now permanently bound to the charcoal.
Over time, microbial action has degraded the oil further and the crude oil odour had
virtually gone in comparison to a very strong odour at the beginning of the experiment.
Mineral content of different source materials
Materials and Methods
The mineral content of seven different hardwood species (ash (Fraxinus excelsior),
birch (Betula spp), beech (Fagus sylvatica), sweet chestnut (Castanea sativa), poplar
(Populus spp.), and oak (Quercus robur)), five soft wood species (spruce (Picea spp),
pine (Pinus silvestrus), cyprus (Cyprus spp) and larch (Larix decidua) and five non-
woody plants (Nettle (Urtica dioica), beet leaves (Beta spp), wheat straw (Triticum
aestivum), barley straw (Hordeum vulgare) and oil seed rape straw (Brassica napus)
was determined using the following procedures.
Demineralisation of charcoals was carried out by weighing 10 g of ground charcoal and
suspending this in 500 ml nitric acid. The pH of the suspension was adjusted to pH 1
and the suspension was left for 24 hours with intermittent stirring to ensure that all
disolvable minerals were removed. The acid was removed by filtering the suspension
using suction filtration. The charcoal on the filter paper was washed with distilled
water three times to remove all acid.
Charcoal Preparation
Charcoals were prepared at 450 C for 6hr in a Carbolite LMF 4 furnace. Starting
materials were wrapped in several layers of aluminium foil prior to charring to exclude
air. Wood charcoals were prepared from trunk wood with a diameter of > 15cm that
had been air dried. Non-woody materials were dried overnight at 105 C.
Ash Content
Ash content of the charcoals was determined using British Standard Method (BSI
2004). Briefly, a heatproof crucible was heated to 550 C for 1hr and then allowed to
cool completely in a desiccator. The crucible was weighed and approximately 1g of
charcoal (<500µm particle size) added. The charcoal was oven dried at 105 C for 24hr,
cooled in a desiccator, weighed and then ashed overnight at 550 C. The ash was cooled
in a desiccator without desiccant and weighed. The percent ash content was determined
using [(m – m )/(m – m )] x 100, where m was the mass of the crucible, m was the
3 1 2 1 1 2
mass of the crucible and dried charcoal and m was the mass of the ash and crucible.
All measurements were carried out in triplicate.
Mineral content
To determine the mineral content of the different charcoals an aqua-regia digest was
prepared followed by an elemental analysis using ICP-OES. Samples were accurately
weighted into 15 cm quartz tubes and stored in a heat proof rack. Samples were ashed
at 460 C for 18 hours. After cooling 0.75 cm concentrated nitric acid followed by 2.25
cm concentrated hydrochloric acid were added to each sample and left for 12 hours.
Subsequently the tubes were heated for 1 hour at 50 C and at every temperature
increment (70, 90 C) till yellow nitrous oxide clears and then finally for a further 2
hours at 110 C. After cooling 0.40 cm H O was added and samples were heated for a
further 30 minutes at 110 C, this process was repeated once more. Finally samples were
made up to 15 cm with water and stored for analysis.
Results
Table 4: Average mineral (K, Ca, Mg and Na) and ash content of 19 different source
materials (n=2)
Source material Mineral content (%) Ash content
K Ca Mg Na Total
Hard woods
Ash 0.460 1.596 0.089 0.007 2.15 4.3
Beech 0.208 0.288 0.052 0.013 0.56 1.1
Sweet Chestnut 0.406 1.010 0.171 0.012 1.60 3.6
Poplar 0.680 1.747 0.238 0.005 2.67 7.0
Willow 0.560 1.769 0.115 0.006 2.45 6.0
Oak 0.667 1.663 0.086 0.015 2.43 5.7
Soft woods
Spruce 0.188 0.165 0.013 0.014 0.40 1.66
Pine 0.215 0.329 0.070 0.003 0.62 1.67
Cyprus 0.284 0.924 0.044 0.003 1.26 3.33
Larch 0.184 0.138 0.031 0.004 0.36 0.60
Non-woody plants
Nettle 14.047 3.909 0.922 0.056 18.93 47.3
Barley straw 3.057 2.071 0.159 0.085 5.37 14.0
Wheat straw 3.266 0.942 0.129 0.093 4.43 12.7
Beet leaves 11.631 3.836 1.253 4.272 20.99 50.0
Oilseed rape 5.087 4.813 0.119 0.206 10.22 34.0
straw
Demineralised samples contained < 0.1 % of either K, Ca, Mg or Na and had ash
contents of < 2%.
Conclusions
Based on their experiments, the inventors have concluded that:-
1) Charred cellulose materials that have a low density are capable of absorbing or
absorbing up to 9x their own weight in oil.
2) Oil absorbing capability of charred and demineralised straw (i.e. non-woody) is
3x greater than charred wood;
3) Continuous macropores play no or only a minor role in the uptake of oil, but
char density is a significant factor that determines oil absorbance;
4) Uptake of oil is governed by the slightly hydrophobic properties of charred
carbon;
) Charcoal (preferably derived from low density cellulose containing materials)
binds oil together to form floating aggregates that are easily removed from the
water’s surface using a fine sieve, net or some other suitable mechanical
removal device;
6) Char applied on top of an oil spill will take up oil preferentially resulting in
oil/char aggregates that contain little or no water;
7) Charred source materials that are particularly useful for oil recovery are those
that are of low density, such as charred paper or straw;
8) Removal of minerals from the charred straw enhances the ability of the char to
absorb oil equivalent to the mineral content of the charred biomass; for barley
straw this figure is 15%, for oilseed rape straw 30% and for nettle straw it is
50%.
9) Use of de-mineralised char for oil recovery would be beneficial as the oil / char
can be processed as normal crude oil;
10) Pre-treatment with small quantities of mineral or vegetable oil will prevent the
composition forming a dust, thus increasing ease of application and preventing
explosion hazards associated with fine powdered materials;
11) Addition of peroxides with the composition will result in the formation of
aerated oily aggregates after application to an oil spill. Aeration of the oil will
enhance the establishment and growth of oil degrading micro-organisms, either
by stimulating those that are naturally present in the environment or ones that
are added to the preparation;
12) Precipitation of iron hydroxides within the charcoal will result in the charcoal
becoming ‘magnetic’ and therefore allowing the composition to be removed
from the environment using magnets;
13) Addition of slow-release fertilisers and vitamins to the composition will result in
a product that allows these minerals to become incorporated into the oily
aggregates, thus enhancing the establishment and growth of oil degrading
micro-organisms, either by stimulating those that are naturally present in the
environment or ones that are added to the preparation;
14) Addition of oil-degrading microbes, especially those of the genus Bacillus, will
allow rapid establishment of an oil degrading culture;
) Oil which has been emulsified within waters is effectively absorbed by the
charcoal products;
16) Sands contaminated with oil can be cleaned by introducing an emulsifying agent
and water, and the subsequently emulsified oils can be removed from
suspension from within the water by amendment with charcoal product;
17) Visual assessments showed that a large proportion of the emulsified oil which
had been absorbed by the charcoal effectively degraded within 14 days with no
further amendments. There is potential to enhance such degradation through
amendment with nutrients (e.g. N, P, K, Mg, Ca) or oxidizing agents (e.g.
peroxides) and/or environmental improvements (e.g. aeration, moisture
control).
Oil absorption of char impregnated with paraffin
Introduction
Charcoal is slightly hydrophobic but, when contacted with water, the water will
normally penetrate rapidly into the charcoal. This leads to the voids inside the char
becoming occupied with water, preventing the uptake of oil. Also, because the specific
gravity of carbon (without the voids) is greater than 1, charcoal will sink when put into
water before it has had the chance to take up oil. As oil normally floats on water, this
will prevent further contact between water and charcoal. In situations where the oil is
dispersed in the water at low concentrations, natural charcoal will absorb mainly water,
making natural char relatively ineffective for the removal of dispersed oil.
There was therefore a need to develop a method that increased the hydrophobicity of
the charcoal significantly, without negatively impacting on the absorption capacity of
the char. Paraffin wax is solid at room temperature and has a melting point of 56 C.
Above 150 C, it is a gas. Paraffin gas easily penetrates into the voids, where it is
adsorbed into the charcoal’s micro and meso-pore structure. Once cooled, paraffin will
solidify thus forming a coating onto the inner charcoal surfaces.
The following experiments were set up to test the effectiveness of paraffin-treated
charcoal for oil absorption, if initially contacted with water.
Materials and Methods
Impregnation of char with paraffin
To impregnate char with paraffin, 10 g paraffin wax was placed at the bottom of a 1500
ml stainless steel container (30cm length; 8 cm diameter) that could be closed with a
tight fitting, but not air tight, steel cap. This allowed gases that were formed to be
released without allowing gases from outside the container to get into the container.
The container was filled with demineralized barley straw char that had been charred at
temperatures >800 C. The particle size of the char was between 0.1 and 2 mm.
Subsequently, the closed container filled with char was placed at a slight angle of 15
degrees inside a muffle furnace (Carbolite, UK) and heated at 200 C for 1 hour. The
char was then left to cool overnight. By shaking samples of the thus treated char with
water, hydrophobicity of the char could be assessed. It was found that the top layer was
not as hydrophobic as the bottom layers, and as a result, the char taken from the
bottom half of the container was used for the following tests.
Absorbance of oil
To compare the maximum oil absorbance of paraffin-treated and non-treated char,
250ml beakers filled with approx. 100 ml water were used. A beaker with water was
placed on a balance and tarred to zero. Subsequently approx. 1 g of oil (Kuwait Crude)
was dropped onto the water surface and the exact weight of the oil added was recorded.
Subsequently, charcoal was added slowly on top of the oil with intermittent swirling of
the water to speed up the process of bringing the charcoal into contact with the oil.
This process was continued till all oil was absorbed from the surface of the water. The
minimum amount of charcoal needed to absorb all the oil was recorded and the
absorbance of the char calculated by dividing the amount of oil absorbed by the amount
of char added. Treatments were replicated three times and the results were analysed
using ANOVA.
To test the oil absorption of the char when contacted with water first, a 250 ml beaker
containing approx. 100 ml water was placed on a balance and tarred to zero. Between
0.2 and 0.3 g of char was added to the water, and the exact quantity of char added was
recorded. The char was left for approx. 5 minutes in the water to allow interaction with
the water to take place. Subsequently, crude oil (Kuwait Crude) was added to the
beaker till the char would take up no more oil. Paraffin-treated and non-treated char
were compared and each treatment was replicated three times. The maximum amount
of oil added was recorded for each replicate and the maximum absorbent capacity of
the char was calculated. Results were analysed using ANOVA.
The test was repeated using salt water (3.5% NaCl) simulating absorbance of oil from
sea water. Results were compared with those obtained with fresh water.
Absorbance of emulsified oil
A qualitative test was set up to assess if paraffin-treated barley char was capable of
removing emulsified Kuwait Crude oil. Oil was emulsified in water using ‘Decon’
(approx. 2 ml Decon to emulsify 5 g oil). The emulsified oil was subsequently divided
into two 500 ml beakers each containing around 150 ml emulsified oil. To break up the
dispersant, the pH of the emulsion was lowered to 1 using concentrated hydrochloric
acid. Approx 1 g of paraffin treated barley char was added to one beaker and the
beakers were left for 8 hours with occasional shaking. Removal of emulsified oil was
assessed visually.
Results
Absorbance of oil from water using paraffin and non-paraffin treated barley char
Table 5: Comparison of maximum oil absorption of paraffin treated demineralized
barley char (paraffin treated DBC) and non-treated, demineralized barley char (DBC).
Absorption of char applied on top of the oil was compared to application of oil to char
that was added to the water first. Results are expressed as g oil absorbed by 1 g char ±
SE. N=3.
Oil absorption (g oil g char)
Treatment P
Oil added first Char added first
DBC 7.57 ± 0.09 0.31 ± 0.07 <0.001
Paraffin treated 5.23 ± 0.16 5.63 ± 0.70 NS
P <0.001 <0.001
Impregnation of char with paraffin reduced the maximum oil absorbent capacity of the
char by around 30% (P<0.001). However, when added to water first the oil absorbance
of non-paraffin treated char declined rapidly to less than 4% of its original oil absorbent
capacity. Paraffin-treated char remained effective at absorbing oil from water with no
significant decline in absorbance. As a result, paraffin-treated char took up 18 times
more oil from the water than non-paraffin treated char (P < 0.001) when the char was
contacted with the water first (Table 5).
Table 6: Comparison of oil absorption by paraffin treated demineralized barley char
from salt water (3.5% NaCl) compared with oil absorption from fresh water. Results are
expressed as g oil absorbed by 1 g char ± SE. N=3.
Oil absorption (g oil g char)
Treatment Oil added first Char added first P
Fresh Water 5.23 ± 0.16 5.63 ± 0.70 NS
Salt Water 5.32 ± 0.64 4.80 ± 0.51 NS
P NS NS
There was no significant difference in oil absorption of paraffin-treated demineralized
barley char from salt or fresh water, irrespective if the oil was added first or if the char
was added first to the water (Table 6).
Absorbance of emulsified oil from water using paraffin treated barley char
Referring to Figure 7, there is shown the removal of emulsified crude oil using paraffin
treated barley char (labelled C-Cure-Oil in the Figure). Oil was emulsified in water
using ‘Decon’ (approx. 2 ml Decon to emulsify 5 g oil).
Conclusions
Paraffin treated char is highly hydrophobic and does not absorb water. Paraffin treated
char is effective at absorbing oil (> 5x its weight in oil). The oil absorbance of paraffin
treated char is not affected by being into contact with water. Oil absorbance of paraffin
treated char is equally effective from salt water as from fresh water. Paraffin treated
char is effective at removing emulsified oil.
In this specification where reference has been made to patent specifications, other
external documents, or other sources of information, this is generally for the purpose of
providing a context for discussing the features of the invention. Unless specifically
stated otherwise, reference to such external documents is not to be construed as an
admission that such documents, or such sources of information, in any jurisdiction, are
prior art, or form part of the common general knowledge in the art.
In the description in this specification reference may be made to subject matter which
is not within the scope of the claims of the current application. That subject matter
should be readily identifiable by a person skilled in the art and may assist in putting
into practice the invention as defined in the claims of this application.
The term “comprising” as used in this specification and claims means “consisting at
least in part of”. When interpreting statements in this specification and claims which
include the term “comprising”, other features besides the features prefaced by this term
in each statement can also be present. Related terms such as “comprise” and
“comprised” are to be interpreted in similar manner.
Claims (61)
1. A method of preparing an oil absorbent composition, the method comprising heating and then de-mineralising a precursor plant material under conditions suitable 5 to produce an oil absorbent composition comprising charcoal, wherein the charcoal comprises non-activated carbon.
2. A method according to claim 1, wherein the oil absorbent composition is contacted with a water repellent substance.
3. A method according to claim 2, wherein the water repellent substance is a solid at room temperature.
4. A method according to either claim 2 or 3, wherein the water repellent 15 substance is selected from the group consisting of: a fat; animal fat; plant fat; a fatty acid; a fatty acid ester; a fatty alcohol; a glyceride (mono-, di- or tri-glyceride); a hydrocarbon; and mineral tar.
5. A method according to claim 4, wherein the water repellent is a hydrocarbon 20 and the hydrocarbon comprises paraffin wax or tar.
6. A method according to any one of claims 2-5, wherein the water repellent substance is contacted with the oil absorbent composition such that it is adsorbed into the micropores and/or mesopores of the absorbent composition.
7. A method according to any one of claims 2-6, wherein the water repellent substance is in a gaseous form when it is contacted with the oil absorbent composition.
8. A method according to any preceding claim, wherein the precursor material 30 comprises, or is derived from, a woody plant material.
9. A method according to claim 8, wherein the precursor material comprises, or is derived from, a hardwood species of plant.
10. A method according to claim 9, wherein the hardwood species of plant is selected from the group consisting of paulownia (Paulowniaceae spp.), aspen (Populus tremulis) and other poplar species. 5 11. A method according to claim 10, wherein the other poplar species are selected from the group consisting of cotton wood (Populus deltoides), balsa wood (Ochroma pyramidalis), Butterwood (Platanus occidentalis), walnut (Juglans regia) and willow
(Salex spp.). 10
12. A method according to claim 8, wherein the precursor material comprises or is derived from a softwood species of tree.
13. A method according to claim 12, wherein the softwood species of tree is selected from the group consisting of conifer (Picea spp.), pine (Pinaceae spp.) and cedar 15 (Cedres spp.).
14. A method according to any one of claims 1-7, wherein the precursor material comprises, or is derived from, a non-woody plant species. 20 15. A method according to claim 14, wherein the precursor material is derived from a plant family selected from the group of families consisting of Brassicaceae, Poaceae,
Amaranthaceae and Urticaceae.
16. A method according to claim 14, wherein precursor material is derivedfrom a 25 genus selected from Brassica or Hordeum.
17. A method according to claim 14, wherein the precursor material is derived from Brassica napus (oilseed rape), Hordeum vulgare (Barley), Triticum aestivum (Wheat), Secale cereale (Rye) Myscanthus (Elephant grass) or Zea mays (Maize).
18. A method according to any one of claims 14 to 17, wherein the precursor material forming the absorbent composition comprises, or is derived from, the stems of a non-woody plant. 35
19. A method according to any preceding claim, wherein the precursor material is heated to a temperature of greater than 280°C, 300°C, 325°C, 350°C, 375°C, 400°C, o o o o o 425°C, 450°C, 475°C , 500°C, 600 C, 700 C, 800 C, 900 C, 1000 C or higher.
20. A method according to any preceding claim, wherein the precursor material is heated at a temperature of between about 280°C and about 1200°C.
21. A method according to any preceding claim, wherein the precursor material is heated at a temperature of between about 350°C and about 800°C.
22. A method according to any preceding claim, wherein the precursor material is 10 heated at a temperature of between about 400°C and about 600°C.
23. A method according to any preceding claim, wherein the precursor material is heated under substantially anaerobic conditions. 15
24. A method according to any preceding claim, wherein the demineralisation step is achieved by contacting the precursor material with an acid for a suitable time period to allow for the removal of mineral ions from the previously heated precursor material.
25. A method according to claim 24, wherein the acid is sulphuric acid, 20 hydrochloric acid or nitric acid.
26. A method according to either claim 24 or claim 25, wherein the pH of the solution is less than 3.0, 2.0 or 1.0. 25
27. A method according to any preceding claim, wherein removal of elements from the oil absorbent composition is achieved by contacting the composition with a buffered solution having a neutral or a slightly acidic pH.
28. A method according to any preceding claim, wherein the concentration of alkali 30 and/or alkali earth metals in the absorbent composition is less than 10% (w/w), less than 5% (w/w) or less than 1% (w/w) of dried material.
29. A method according to any preceding claim, wherein the total concentration of potassium, magnesium, calcium and/or sodium is less than 10% (w/w), less than 5% 35 (w/w) or less than 2% (w/w) of dried material.
30. A method according to any one of claims 24 to 29, wherein, after demineralisation, the method comprises a step of separating the resultant absorbent composition from the acid. 5
31. A method according to claim 30, wherein the method comprises a step of separating the resultant absorbent composition from the acid by filtration or centrifugation.
32. A method according to claim 30 or 31, wherein, following separation from the 10 acid, the method comprises adjusting the pH of the composition until the pH indicates that the majority of the acid has been substantially neutralised.
33. A composition, suitable for absorbing oil, obtained from the method according to any one of claims 1 to 32.
34. A composition, suitable for absorbing oil, comprising charred charcoal comprising, or being derived from, plant material, wherein the charcoal has a density less than 0.2kg/L and a mineral content of less than 5% (w/w) of dried material and the charcoal comprises non-activated carbon.
35. A composition according to either claim 33 or claim 34, wherein the density of the absorbent composition is less than 0.17 kg/L, 0.15kg/L or less than 0.14kg/L.
36. A composition according to any one of claims 33 to 35, wherein the mean 25 particle size of the absorbent composition is between 0.01mm and 50mm, or between about 0.01mm and 25mm, or between about 0.1mm and 10mm, or between 0.1mm and 5mm, or between 0.1mm and 1mm is effective.
37. A composition according to any one of claims 33 to 36, wherein the composition 30 comprises up to 10% (w/w) mineral oil or vegetable oil.
38. A composition according to any one of claims 33 to -37, wherein the oil absorbent composition comprises a water repellent substance, which comprises lipid.
39. A composition according to claim 38, wherein the repellent is selected from the group consisting of: a fat; animal fat; plant fat; a fatty acid; a fatty acid ester; a fatty alcohol; a glyceride (mono-, di- or tri-glyceride); a hydrocarbon; and mineral tar. 5
40. A composition according to claim 39, wherein the repellent is a hydrocarbon and the hydrocarbon comprises paraffin wax or tar.
41. A composition according to any one of claims 33 to 40, wherein the absorbent composition is magnetic, optionally comprising, iron, iron oxide or iron hydroxide.
42. A composition according to any one of claims 33 to 41, wherein the absorbent composition comprises an oxygen-releasing agent.
43. A composition according to claim 42, wherein the oxygen releasing agent is 15 sodium peroxide or calcium peroxide.
44. A composition according to any one of claims 33 to 43, wherein the absorbent composition further comprises slow-release fertilisers that contain nitrogen, phosphate, or potassium, and/or a selection of micro-nutrients as well as vitamins to 20 enhance the growth of hydrocarbon-degrading microorganisms.
45. A composition according to claim 44, wherein the micro-nutrients comprise Fe,
Cu, Co and/or Zn. 25 46. A composition according to any one of claims 33 to 45, wherein the absorbent composition further comprises a community of oil-degrading bacteria.
47. A composition according to claim 46, wherein the oil-degrading bacteria belong to one or more genera selected from the group consisting of:Pseudomonas; Bacillus; 30 Staphylococcus; Acinetobacter; Kocuria; and Micrococcus.
48. Use of the composition according to any one of claims 33 to 47, for absorbing oil. 35
49. A method for absorbing oil from an oil-contaminated material, the method comprising contacting an oil-contaminated material with the oil absorption composition according to any one of claims 33 to 47, and allowing the oil to be absorbed by the composition.
50. A method according to claim 49, wherein the oil-contaminated material is a 5 fluid.
51. A method according to claim 50, wherein the fluid is water.
52. A method according to claim 49, wherein the oil-contaminated material is oil- 10 contaminated sand or bituminous sand.
53. A method according to claim 52, wherein the method comprises introducing an emulsifying agent and water, and the subsequently emulsified oils can be removed from suspension first by acidification and subsequently from the water by contacting with 15 the composition.
54. A method according to any one of claims 49 to 53, wherein the method comprises a step of separating the oil absorption composition from the oil- contaminated material.
55. A method according to claim 54, wherein the separation step comprises use of a sieve, suction sweeper, a fine-meshed net or a magnet, a mop consisting of ropes or any other physical device designed to remove oil from a water surface. 25
56. A method according to any one of claims 49 to 55, wherein the method comprises a step of recovering the absorbed oil from the absorbent composition.
57. A method according to claim 1, substantially as herein described with reference to any example thereof.
58. A composition according to claim 33, substantially as herein described with reference to any example thereof.
59. A composition according to claim 34, substantially as herein described with 35 reference to any example thereof.
60. Use according to claim 48, substantially as herein described with reference to any example thereof.
61. A method according to claim 49, substantially as herein described with 5 reference to any example thereof.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB201105961A GB201105961D0 (en) | 2011-04-08 | 2011-04-08 | Oil absorbent composition |
GB1105961.5 | 2011-04-08 | ||
GB1117521.3 | 2011-10-11 | ||
GB1117521.3A GB2489764B (en) | 2011-04-08 | 2011-10-11 | Oil absorbent composition |
PCT/GB2012/050683 WO2012136981A2 (en) | 2011-04-08 | 2012-03-28 | Oil absorbent composition |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ616152A NZ616152A (en) | 2014-12-24 |
NZ616152B2 true NZ616152B2 (en) | 2015-03-25 |
Family
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