Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF INVENTION
PEAT PELLETS
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SFIELD OF INVENTION
The present invention relates to pellets formed
from peat.
BACKGROVND TO THE_INVENTION
Oil film contamination of water bodies can cause
heavy damage to aquatic life since the oil film retards
penetration of oxygen into the water and oil washed up
on beaches can destroy foreshore marine life.
A variety of proposals have been made to remove oil
films from water. One such method involves the use of
oil-absorbent materials which can be spread onto and
float on the oil covered water to absorb the oil film.
The oil-absorbent material then can be retrieved and the
oil recovered or otherwise disposed of.
It has previously been suggestea to employ peat in
powdered form as such an oil-absorbent material. Peat,
however, is hydrophilic in the natural state and hence,
although peat absorbs oil on the surface of the water, a
quantity of water also is absorbed, often causing the
peat to sink. Accordingly, it has been considered
necessary, therefore, to increase the hydrophobicity of
the peat for use as an oil absorbent.
One such proposal is con~ained in Canadian Patent
No. 956,928 wherein it is indicated that peat with a
decreased moisture content becomes hydrophobic and,
accordingly, the patent proposes to decrease the water
content of peat to below 10 wt.~ for use as an oil-
absorbent material.
Another proposal is contained in Canadian Patent
No. 1,160,201, wherein peat, at its natural moisture
content of about 60 to 80 wt.%, is mixed with an
alkaline earth metal material, notably calcium
carbonate, the peat is partially dried to a moisture
content of about 25 to 35 w~.%~ the partially dried peat
is mixed with further alkaline earth metal material, and
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the treated peat is dried further to a final moisture
content of about 5 to 10 wt.%. The product is said to
have a high hydrophobicity and to be capable of
absorbing up to 20 times its own weight in oil. Treated
peat prepared in accordance with this process is
commercially available under the trade name "OCLANSORB"
from Hi-Point Peat Ltd., Newfoundland, Canada.
- Although hydrophobic peat is e~Efective in absorbing
oil from oil-contaminated water bodies and from other
oil-contaminated surfaces without the concomittant
problem of water absorbtion, a major problem lies in the
physical form of the peat, namely its dry powder form.
The dry peat is light and readily becomes airborne,
rendering it often difficult to apply effectively to a
large body of open water without significant wind
losses, and also providing a significant fire hazard on
storage and during indoor use.
SUMMARY OF INVENTION
In accordance with the present invention, these
prior art problems are overcome by providing peat in the
form of pellets. By providing the peat in pelleti~ed
form, the prior art problems of wind-borne losses and
the fire hazard of dry powdered material are overcome,
albeit at a moderate loss of absorbency~
The peat pellets may be formed using any desired
pelletizing proceduxe. Generally, the peat is provided
at an intermediate moisture level, gen~rally in the
range of about 35 to about 60 wt.~, pellets are formed
from the peat at the intermediate moisture level, and the
pellets are dried to the final moisture content,
generally about 5 to about 10 wt.%.
It has been surprisingly found that the manner of
drying the peat affects the absorbency characteristics
of t~e product. If the peat is oven dried at a
temperature of at leas~ about 100C to its final
moisture content, the product is hydrophobic as well as
possessing oil absorbency properties while, if the peat
is air dried at a temperature helow about 100C to its
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final moisture content, the product is hydrophilic~ as
well as possessing oil absorbency properties.
This choice of propexties enables the peat pellets
to be employed in a variety of absorbency operations.
When the peat pellets are hydrophobic, the pellets may
be used to absorb organic materials, such as oils, while
the absorption of water is inhibited. When the peat
pellets are hydrophilic, the pellets also may be used to
absorb aqueous media, such as in a kitty litter
application or in the clean-up of acid spills, or may be
used as a garden mulch.
It has further surprisingly been found that the
inclusion of calcium or other alkaline eart~ metal
sulphate in the pellets enhances the absorbency
characterlstics of the pellets and introduces fire
retardancy in the pellets. The calcium carbonate
additive suggested in Canadian Patent No. 1,160,203 does
not achie~e either result in the pellets of the
invention.
The calcium sulphate also acts as a binder to
enhance the integrity of the pellets. Another useful
property that the presence of the calcium sulphate
introduces is the ability to break oil-in-water
emulsions. Such pellets then are useful in the
treatment of emulsions to break the same and absorb the
resulting freed oil.
When such calcium sulphate, or other alkaline earth
metal sulphate, is present, quantities may vary widely,
generally from about 1 to about 35 wt.%, preferably
about 5 to about 25 wt.%.
BRIEF DESCRIPTION OF D~AWINGS
Figure 1 is a graphical representation o~ the
variation of oil absorbency with gypsum content and
initial moisture content in air-dried peat pellets;
Figure i is a graphical representation of the
variation of water absorbency with gypsum content and
initial moisture content in air-dried peat pellets; and
Figure 3 is a graphical repreaentation of the
change in bulk density of air-dried peat pellets with
initial moisture content.
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GENERAL DESCRIPTION OF INVENTION
Muskeg forms a significant proportion of the
landmass of Canada, about 12 percent, and comprises a
s~rface mat of mosses, sedges and/or grasses, beneath
which is a mixture of paxtially decomposed and
disintegrated organic material, commonly referred to as
"peat".
Peat can vary widely in its physical
characteristics and three types have been identified,
namely material composed chiefly of soils of an
amorphous granular base, material chiefly made up of
fine fibres and material predominantly of wood particles
and coarse fibres. Within this broad classification,
sixteen categories of peat have been identified, ranging
from the coarsest woody, coarse~fibrous peat containing
scattered wood chunks to the finest amorphous-granular
peat. The present invention is use~ul with all types-of
pe t, but has particular application to types which are
predominantly fibrous in character, since peat in this
form is readily formed into useful pellets.
The peat is provided at an intermediate moisture
level of about 30 to about 60 wt~%, typically about 50
to 55 wt.%. This moisture level may be achieved by
drying the peat from its natural moisture level or by
moistening previously-dried peat. At this moisture
level the peat may be readily pelletized using a pellet
mill. Calcium sulphate may be added to the peat prior
to pelletizing to assist in binding the pea~ and also to
act as a fire retardent and to affect the absorbency
characteristics of the pellets. Other materials may be
used as binders for the pellets in place of the calcium
sulphate, as desired, for example, bentonites and
lignosulphonates. Surfactants also may be added to
decrease oil absorbency.
The bulk density and absorbency properties of the
pellets are affected by the initial moisture content of
the peat. As ~he initial moisture content of the peat
which is pelletized increases, the bulk density of the
peat pellets obtained decreases. As the bulk density of
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the pellets decreases, the absorbency of the pellets
increases. Addition of calcium sulphate increases the
bulk d~nsity. With increasing moisture content, the
q~ality of the pellet in terms of pellet strength
decreases while the volume of fines produced increases.
The greater ~he strength of the pellets, the more
resistant the pellets are to disintegration upon
subsequent handling~
The pellets may be providea in any desired size
convenient to handling and the desired end use.
&enerally, the pellets may have a diameter from about
1/8 to about ~ inch and a length to diameter ratio of
about 0.5:1 to about 2:1.
The pellets then are dried to their final moisture
lS content of about 5 to about 10 wt.%. As not~d
previously~ peat naturally possesses oil absorbency.
The manner of drying, however, affects the other
properties obtained~ Oven drying at a temperature above
about 100C imparts hydrophobicity to the pellets, while
the oil absorbency properties re~ain.
Air drying of the peat pellets at a tsmperature of
below about 100C to the final moisture content does not
impart hydrophoblcity to the pellets and the
predominantly hydrophilic properties are retain2d along
with the oil absorbency properties. By choice of the
specific variables, desired water/oil absorbency
properties may be provided in the product.
The peat pellets of the present invention may be
put to a variety of us~s. Pellets having predominantly
hydrophobic properties may be used to absorb organic
liquids, for example, oil spills from aquatic bodies,
without the attendent dusting and flammability problems
of the prior art.
The peat pellets which have hydrophilic properties
are also useful in treating oil contaminated waste
water. Hydrocarbon-contaminated waste water is produced
as a by-product of oil recovery and generally is
unsuitable for any purpose other than injecting back
into the reservoir or into ano~her geological formation.
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Long term disposal of such waste water is a problem due
to reservoir plugging by the contaminated water.
As to the formation plugs, injectivi y decreases
and the volume of water then can be disposed of per unit
time decreases. Ultimately the capacity of the
formation to take up water is less than the volume that
must be disposed of. At this point, the well must be
serviced or a new well drilled, both cos~ly
alternatives.
Oil/water emulsions are frequently used in
machining. Such emulsions have a finite life and, after
a period of time, lose their effectiveness as cutting
oils in the fabrication of metal parts. Prior to
disposal, most cutting oils are tr~ated with acid in
holding tanks, breaking the emulsion. The oil floats to
the top of the tank and is decanted, while the water is
disposed of into the sewage system. This procedure
suffers from ~he physical space requirements of the
holding tanks and the necessity for a long holding time
to permit the emulsion to break and separate.
In accordance ~ith one aspect of the present
invention, the peat pellets of the invention are
utilized to remove free hydrocarbon from contaminated
water andr when the peat pellets also contain calcium
sulphate or other alkaline earth metal sulphate~ to
break oil/water emulsions. In this aspect of the
invention, the material to be treated is passed through
a bed or a series of beds of peat pellets. As the
aqueous medium passes through the bed, emulsions are
broken by the calcium sulphate and the hydrocarbon phase
is absorbed by the peat pellets, to provide a clean
aqueous product. Peat pellets having hydrophilic
properties are particularly useful in this aspect of the
inventlon .
The peat pellets of the invention having
hydrophilic properties also may be used as an absorbent
for aqueous media. For example, the pellets may be used
as a kitty litter product in place of the clay-based
products used cor~ercially. Hydrophilic peat pellets
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also can be used to clean up aqueous chemical spills,
for example, acid spills.
In addition, hydrophilic peat pellets from which a
blnder is absent tend to disintegrate and return to
their original fibrous form when contacted with water.
For this reason, such hydrophilic peat pellets have
horticultural use as a garden mulch, which can be
readily distributed and then disintegrates to f ibrous
form upon exposure to water.
EXAMPhES
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A series of experiments was carried out to
investigate the relationship between initial moisture
content prior to pelletization, calcium sulphate content
of the pellets, bulk density of pellets and the
oil/water absorbency properties of the pellets. The
experiments were perfor~ed on peat from Alberta, Canada
which was classified as fibrous. The peat had an
initial water content of 35% and water was added to the
pelletization moisture level. The peat was pelletized
to pellets dimensioned ~ inch using a labora~ory
pelletizer and the pellets were air dried at a
temperature of about 22C to a final moisture con~ent of
about 8 wt.%.
The oil absorbency results were plotted graphically
-and appear as Figure 1. As may bP seen from this data,
the higher the initial moisture, the more absorbent the
final pellet with oil absorbency increasing from a low
of 0.2 to a high of 0.85 for moisture contents of 34 and
55% respectively. In addition, the da~a shows that the
presence of the calcium sulphate also affects oil
absorbency to some degree.
The water absorbency results were plotted
graphically and appear as Figure 2. As may be seen from
this data, the water absorbency properties are
significantly higher than for oil, with the property
again increasing with increasing moisture conten~ of the
pelletizea peat. Again, the presence of the calcium
sulphate affects water absorbency to some degree.
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In one experiment, air dri~d pellets were further
dried at 100C for 24 hours and thls heat treatment
decreased the water absorbency of the pellets from 2.8
to 0.4 while the oil absorbency remained the same.
The bulk density of the pellets obtained in the
absence of added gypsum was determined for variations in
initial moisture content of the peat which is pelletized
and the results plotted graphically as Figure 3. As
seen therein, as the initial moisture content increases,
the bulk density decreases.
Example 2
A laboratory filter arrangement was set up
comprising a paix of cylinders each 10 cm in diameter
and 60 cm long and filled with air dried peat pellets
having a moisture content of about 8~, containing
calcium sulphate in the amount of 5~ and sized ~ inch.
Liquid was pumped up through the first filter bed r d~wn
through the second fil~er bed and then through a sand
filter at the discharge end of the second filter bed to
remove fine peat particles washed from the surface of
the pellets.
The filter was tested with two liquids, namely
Aberfeldy (Alberta, Canada~ production water and a lO~
cutting oil emulsion. The Aberfeldy production water
was a black opaque liquid. 60 litres of this li~uid
were passed through the filter at a flow rate of 1
L/min. The discharge from the filter was transparent
and light ~rown in colour7 signifying substantial
removal of hydrocarbons from the production water.
The cut~ing oil was an opaque white liquid. lO
litres of this liquid was passed through the filter at a
flow rate of 1 L/min. The discharge from the filter was
a pale transparent yellow liquid, signifying breaking of
the emulsion and removal of the cutting oil. The yellow
colour was tXought to be imparted by humic acid and
infrared analysis of the filtered water did not indicate
any residual cutting oil ih the water.
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SUMMARY OF DISCLOSURE
In summary of this disclosure, the present
invention provides peat in a novel form, namely
pelleti2ed form, which is useful in a variety of
absorbency property applications. Modifications are
possible within the scope of this invention.
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