Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO93/15833 PCT/NO93/~20
`" 21272~2
OIL-ABSORBENT FIBER PELLET5.
By the use and transport of different oil products it is
almost impossible to avoid some contamination of the envi-
- ronment under different conditions. Small amounts of oil
from land-based plants can normally be handled easily and ;~
efficiently, but the situation grows much worse when for
instance, ocean-going tankers run aground with big leakages
as a consequence. Such incidents have previously occurred
both in Alaska and on the coast of Britanny, France and in
addition to the enormous costs involved in cleaning up the
beaches and the shorelines, said incidents can also result
in detrimental long-term effects on the vegetation and the
life of marine animals and birds.
It is obvious from the serious consequences that there is a
need for more efficient tools to handle oil spills at open
sea, and preferably before the oil products have had the
time to spread over large areas~ Today, lenses are mostly
used to keep the oil within a certain area, but they have
their limitations when the wind is strong and the sea is
heavy, that is, weather conditions when ships are most
likely to be wrecked.
Chemicals with surface-active agents added, are also used
and they will help to dissolve or disperse the oil in the
water. Among the experts there are mixed opinions about the
merits of these products since they are organic in charac-
ter and may have toxic effects. In order to have a signifi-
cant effect great quantities will also be needed, and the
weather conditions are sometimes so extreme that the chemi-
cals cannot be distributed on the ocean surface. All these
limitations indicate that this is not a completely satis-
factory solution to the the problem considering therequirements regarding environmental control.`
W093/15833 212 ~ ~ sæ PCI/NO93/00020
: i '
There are also known fiber products which may be used to
absorb oil and similar products, and such products are also
sold on a commercial scale. According to the government
authority, responsible for these matters in Norway, these
products mostly consist of bark, but they have the drawback
that they cannot be used in open sea, but only in the beach
zone. A difficulty with bark is also that it contains a
significant amount of water-soluble substances, and also ~-
under mechanical stress they will break down to very small
particles, being difficult to collect without very expen-
sive procedures. The bark products can be mechanically
strengthened by being compressed into briquets, but this `
will reduce the porosity of the material and hence also the
amcunt of oil being absorbed.
Products of unbleached and bleached cellulose (chemical
pulps) have also been suggested for this purpose. These
products are mostly hydrophylic by nature, and therefore it
has been necessary to add significant amounts of chemicals
like wax emulsions, resins, alum etc. in order to make the
product hydrophobic. This is absolutely necessary if the
product is intended for use in open sea. Such products are
mentioned in N0 Patent No. 117.169, and the application of
organic materials like saw dust with a particle size pre-
ferably from 0,25 to 2 D iS described therein. In thiscase chemicals like methyl-trichloro-silane are used in
order to achieve a hydrophobic effect, and no attempt is
made to utilize the chemicals which is present in the wood
itself.
Similar products are described in N0 Patent No. 118.786,
also based upon organic materials such as saw dust. In this
case the material is treated with paraffin-like hydrocar-
bons and/or animal or vegetable oils with an emulsifier.
There is no mentioning of the use of the chemicals in the
wood, nor is it described how to make particles with a
suitable size and open capillaries.
WO93/1~33 PCT/NO93/ ~ 20
2i~7~2
Fiber products are also described in N0 Patent No. 137.688.
Rosin sizing is here used in order to make the particles
suitable for oil absorption. In the main claim it is stated
that all types of pulp may be used, but in most examples
kraft pulp has been used. This is a pulp manufactured by
means of an alkaline process which will efficiently remove
the chemicals in the wood which are utilized in accordance
with the present invention. Accordingly, the idea that the
chemicals in the wood might be used to attain a hydrophobic
effect, has apparently not occurred to the inventors of
~0 patent No. 137.688. It should also be added that the
density of the product are given to be in the range of
3,2 - 24 kg/m3, and this is much lower than the density of
the particles made in accordance with the present inven-
tion.
The problem may be expressed as how to make porous partic-
les with sufficient strength not to disentegrate in open
sea under the mechanical strains involved and with a hydro-
phobic sur-face which will permit only a minimum of water
to be absorbed. It should be added that it is virtually
impossible to prevent water from penetrating in the vapour
phase. This amount will be a function of the water tempera-
ture, its vapour pressure and also the time the particles
are in contact with the water.
In US Patent No. 4.343.680 it has been disclosed that it is
possible to use wood species with a high content of extrac-
tives such as pine, to achieve a material which is hydro-
phobic, but oil-absorbing. In this case a limit of 3,0 ~ by
weight based on the weight of the wood extractable with
ether has been mentioned, and it has also been specifically
mentioned that a thermo-mechanical pulp of pine might be
used. It is true that in this patent the chemicals in the
wood are utilized, but the examples also indicated that it
has been necessary to treat the material at lOS'C for 16
hours in order to get the desired effect. In this case the
WO93/1~33 PCT/NO93/~20
21272~
material is then fed to a fiberizer in order to separate
the material into single fibers, and then packed in bags or
pressed into bales. Accordingly, there is no comments about
how to make spherical particles which are hydrophobic and
oleophyllic in a single process stage with a process time
in the order of minutes, and where the pulp deliberately is
treated with the goal to produce particles with a suitable
size.
From the technology described in US Patent No. 4.343.680 it
must be regardèd as surprising that it is possible to make
hydrophobic and oleophylic fiber pellets in one integrated
process stage, with wood chips as raw material and with a
heat treatment of only a few minutes at high temperature.
It is also surprising that it is possible to make pellets
which are approximately spherical in form by letting the
particles rotate during the drying process. Rotating driers
- are well known from the cement and fish industry, and they -~
are normally arranged with a certain inclination to convey
the particles by gravity from the inlet to the outlet .
In real life there will always be variations in the extrac-
tive content of the trees, for instance between the outer -
layers of the tree and the core. Such variations will also
normally occur from summer to winter. To compensate for
these variations, which may give undesirable quality varia-
tions in the product, it may be necessary to add small
amounts of chemicals contributing to the hydrophobic
effects. ~t should be clearly understood, however, that
this amount should be much smaller than the rosin content
present in the wood.
The simplest process will be to treat wood chips rich in
extractives in modern refiners without use of chemicals ,
but at higher temperatures. In such refiners the tempera-
tures will frequently be between 115- and 130-C, but tempe-
ratures down to about 100- may be accepted during the defi-
W093/1~33 PCT/No93/ ~ 20
212~i?,~2`
bra'ion process. This thermo-mechanical pulp will be dried
at higher temperature while rotating, and the pulp is natu-
rally acidified by the organic acids liberated during the
drying process and the subsequent storage. It will however,
also be possible to make a satisfactory product by impreg-
nating the chips with chemicals such as alkali and/or sul-
fite. The pulp will in this case be called CTMP (Chemi-
Thermo-Mechanical-Pulp), and the advantage of this process
is that the defibration will be more complete and the
average fiber length greater. In order to get a hydrophobic
surface in this case, it is essential that the pulp is not
washed, and further that it is acidified with strong acids
such as sulphuric acid or hydrochloric acid before the
drying process is initiated.
l3~ca~Dle l:
An assortment of Norwegian pine (Pinus Silvestris) with an
outer diameter of 20 cm and with an extractive content of
2,6% based upon the wood weight as determined with dichloro
methane, was chipped in the normal way before making thermo
mechanical pulp being a modern high yield pulp. The chips
were moistened with steam and run through double disc
refiners in two stages to a Canadian Freeness of about 150.
This is a measure of the particle size of the pulp and is
mainly a function of the energy consumption. The pulp left
the refiner at a consistency of about 20%, and was then
transferred to a cement mixer, where hot air was blown into
the mixer while rotating. The main part of the pulp was
3~ converted to spherical particles of varying sizes, and
after complete drying and storage at a somewhat higher
temperature for some days, the particles had developed a
hydrophobic surface enabling them to float on water for a
couple of days. At the same time the particles willingly
absorbed oil in an amount corresponding to several times
the weight of the fibers. `
~ ~.
WO93/15833 PCT/No~3/~20
2127252
_xample 2.
A load of pine from Zambia (Pinus Kesiya) was treated in
the same way as described in Example 1, but the Freeness
was not reduced to more than 300 CSF. Under these condi-
5 tions it was more difficult to form the fibers into partic- `~
- les, and it was also more difficult to make the surface
completely hydrophobic. The reason is probably the fact
that tropical pine species contain less extractives than
the pines growing in the temperate areas. It was also clear
that the ability to form spherical particles during drying,
is related to the specific surface of the fibers, and this
is increased on increasing the energy consumption which
also will reduce the Freeness level.
Bxa~Dle 3.
A load of Norwegian pine like the wood used in Example 1
was impregnated with 1% NaOH and 3% sodium sulfite. The -
impregnated chips were treated in the refine at 115-C in
two stages as mentioned in a preceding paragraph to a
Freeness of 200 CSF. The solid content from the refiners
was about 22%. The pulp was dried at llO-C to a solid
content of 10% under slow rotation. The pulp was then
stored for a few days at a slightly elevated temperature.
The greater part of the particles were spherical in shape,
and all of them developed a hydrophobic surface.
It should be emphasized that the curing at elevated tempe-
rature after the drying was required due to the shortcoming
of the laboratory drying equipment. On an industrial scale
an optimum air temperature and drying conditions may be
selected, and the after-curing will then not be necessary.
It should also be emphasized that the present invention
will not be limited to the examples which are only meant to
illustrate how the product can be made. On an industrial
scale continuous, rotating driers will obviously be used,
such as the opes used in the cement industry, but with
W093/15833 21 27 2~2 PCTtNO93/ ~ 20
other temperatures, because the fibers are combustible. To
avoid overheating the moist material might be dried in a
co-current manner with high temperature drying air, even if
this is not the most effective procedure from an energy
S point of view. It will, however, be possible and efficient
to use temperatures much higher than lOO-C.
