Note: Descriptions are shown in the official language in which they were submitted.
106Z6Z7
The present invention concerns the removal of oil
from an oil in water emulsion
According to the present invention we provide a method
for the removal of oil from an oil in water emulsion which
comprises passing the emulsion through a fibrous stxucture
comprising fibres having finely divided particles which exhibit
oleophilic and hydrophobic properties penetra~ing their outer
surfaces, and removing the coalesced oil droplets 50 formed.
` The fibres, e,g, continuous filaments of staple fibres,
may be homofibres to which the particles have been caused to
adhere and penetrate their surfaces by subjecting the homofibres
to surface heat and/or plasticiser treatment(s). Alternatively,
the fibres may be homofibres with a non-fibre forming resinous
or polymeric coating thereon,which coating when sub~ected to
`~ heat and/or plasticiser treatment(s) and having particlen
applied;thereto allows them to penetrate and adhere.
Most desirably, however, the fibres are conjugate fibres.
By the expression "conjugate fibre" is meant a spun, especially
a melt spun, fibre (i.e. a continuous filament or a staple fibre)
composed of at least two fibre-forming polymeric components
arranged in distinct zones across the cross-section of the fibre
and substantially continuous along the length thereof, and
wherein one of the components has a melting temperature
~i significantly lower than the melting temperature (s) of the
other components and is located so as to form at least a portion
of the peripheral surface of the fibre.
Therefore, according to a preferred embodiment of the
invention, the method utilizes a fibrous structure comprising
! oriented, conjugate fibres(as hereinbefore defined~, the
component of lower melting temperature having finely divided
particles which exhibit oleophilic and hydrophobic properties
penetrating its outer surface.
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~0626Z7
Conjugate fibres having two components are preferred.
The most preferred type of bicomponent fibre is one wherein a
component of low melting temperature forms a sheath about
another component serving as a core; although a bicomponent fibre
wherein a component of low melting temperature is one o~ kwo
components arranged side-by-side may also be used,
- The polymeric material of the low melting point
component has a melting point at least 10C, preferably at least
20C, below that of the other component of the fibre.
The fibrous structure may be in the form of a knitted
fabric, a woven fabric or a non-woven fabric, the latter being
preferred, Particularly desirable fibrous structures are melded
-i fabrics produced from staple fibres or oriented, i.e. drawn,
sheath/core heterofilaments. Such melded fabrics may either be
point-bonded or area-bonded, Any one fibrous structure may
comprise more than one layer of fabric.
,' The preferred particles are silane-coated silica
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particles, although other particles which exhibit the combined
properties of oleophilicity and hydrophobicity may be used, The
average size of particle is preferably at least 0.1 micron, The
"average size of particle" indicates the largest cross-sectional
-~ dimension of a particle,e.g. the diameter in the case of a
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spherical particle. Most desirably the particles have an average
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size of one micron or less,
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1062627
~ he degree of hydrophobicity of the fibre~ should be
such that the fibrous structure effects a water contact angle
of at least 110 and preferably greater than 140. The magnitude
of the contact angle is largely dependent on the type of hydro-
phobic particles used and its concentration per unit area at the
surface of each fibre. The oleophilic nature of the particles
exposed on the fibres is such that the oil comes into contact
with, and temporarily adheres to, the particles and the oil
droplets then coalesce and pass through the fibrous structure.
The process is thought to be enhanced by the surface roughness
of the fibres due to the presence of the particles,
The porosity of the fibrous structure is chosen such
that the probability of the oil particles contacting the fibres
is as high as possible without creating too high a pressure drop
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across the fibrous structure. Of the preferred fibrous
structures, point-bonded melded fabrics, being more tightly
packed, have a much higher pressure drop than area-bonded
melded fabrics. With both point-bonded and area-bonded melded
fabrics, the pressure drop is usually less than 50 cm of water
at hydraulic flows up to 16m3 per hour per square metre of
fabric, However the pressure drop will increase above this
figure as the hydraulic flow and/or oil throughput is increased,
By "point-bonded fabric" we mean a fabric in which the
fibres have small discrete regions in which the fibres are
strongly adhesively bonded to each other, which regions are separ-
ated from each othex by less strongly bonded, or even unbonded,
regions.
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By "area-bonded melded fabric" we mean a fabric the
fibres in which are adhesively bonded to each other at
substantially all cross-over points throughout the thickness
and over the whole area of the material.
Particularly efficient fibrous structures are those
comprising two or more superimposed area-bonded melded fabrics
followed by one or more point-bonded melded fabrics. With a
fibrous structure comprising three superimposed area-bonded
meldea fabrics followed by a superimposed point-bonded melded
fabric it is possible to achieve in excess of 97% and some~imes
` in excess of 9~/O reduction in oil concentration, after allowing
sufficient time, for example 4 to 8 minutes for gravimetric
separation of the coalesced oil droplets, by a singla pass
through the fibrous structure at hydraulic flows up to 9 2m3
per hour per square metre of fabric.
With other fibrous structures such as two superimposed
area-bonded melded fabrics followed by a superimposed point-
bonded melded fabric or two superimposed area-bonded fabrics, the
efficiency is not as high. Nevertheless, as the pressure drop
through such fibrous structures will ~e lower, they may be
preferable when high loadings are required.
In order that the fibrous structures described herein
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can operate with maximum efficiency it is desirable that the fl~w
of oil in water emulsion through the structure is substantially
, uniform across the structure. Conveniently this can be achieved
I by passing the emulsion through a suitably shaped and dimensioned
sheet or block of an open-cell expanded plastics material located
immediately upstream of the fibrous structure.
Apart from serving to distribute the flow substantially
across the fibrous structure~ the presence of the cellular
plastics material on the upstream side of the fibrous structure
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serves to prevent extraneous matter e g solid particles and
large oil droplets from entering, and causing blockage in
~he fibrous structure.
A particularly desirable expanded plastics material for
this purpose i5 a hydrophilic plastics material such as a hydro-
philic polyurethane foam.
The fibrous structures used in the invention may
have any suitable shape. Though the fibrous structure may be
in the for~ of a sheet or block having substantially planar faces,
the-fibrous structure may have a tubular form. In the latter
case the oil in water emulsion can either be passed from inside
to outside or from outside to inside of the fibrous structure.
In practice, however, when the fibrous structure is in the form
of a tube, we find it more convenient to pass the oil in
water emulsion into the inside of the tube and allow it to
flow through the wall of the tube. We have found that by
adopting this expedient, the oil/water mixture after passing
through the fibrous structure tends to adopt a linear flow and
` this encourages the coalesced oil droplets to separate from the
water by gravity,
The method of the present invention can be used with
either vegetable or mineral oil emulsions. The method has been
; founded to be particularly effective for achieving caalescence
of a variety of both vegetable and mineral oil emulsions for
example emulsions from the cleaning of tankers or storage
vessels used to transport mineral and vegetable oils, ballast
water in crude oil tankers and oil containing coolants.
The invention will now be described with reference
to the following Examples.
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1062627
EXAMPLE 1
A point-bonded, melded fabric of 137 gm, per square
metre, produced from staple fibres of oriented, i.e. drawn,
sheath/core heterofilaments in which the core(5~/0 by weight of
total weight of filament) was polyethylene terephthalate of
melting point 257C and the sheath was a copolymer of poly-
ethylene terephthalate and polyethylene adipate (85:15 mole
ratio) o~ melting point 220~C, was passed through a 2%
dispersion of silane~coated sîlica particles ~"Silanox 101",
Trade ~ark; manufactured by Cabot Corporation; primary particle
size 7 milli-midrons; BET surface area 225 m2/gm) in trichloro~
ethylene. The dried fabric was held at constant area on a pin
stenter frame whilst being heated at 217C for ten minutes, and
finally rinsed with water to remove loosely adhering particles.
Dropstof water placed on the dried fabric had a mean contact
angle of 15S,
This fabric was designated Fabric A,
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An area-bonded, melded fabric of smiliar construction
, was treated in a similar manner, This fabric was designated
Fabric B.
~ A coalescer was produced by forming a four component
`~ lay-up by superimposing one piece of Fabric A and three pieces
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of Fabric B in that order. The fibrous structure so formed was
~`, sufficiently strong to allow it to be fixed in position as a
common wall between two reservoirs X and Y, the area-bonded
-~ face of the structure i.e. Fabric B facing reservoir X and the
i point-bonded face of the structure i.e, Fabric A facing
reservoir Y.
Each reservoir was fitted with a floating arm take-off
which could be adjusted so that any oil floating to the surface
of the oil/water emulsion in the reservoir could be skimmed off.
lO~Z627
Water from the mains was fed by a rotometer into
reservoir X. Oil was fed from a barrel directly into the
stream of water entering the reservoir and an oil in water
emulsion was produced containing 236 ppm of oil, When the
reservoir X had filled up, the flow into the reservoir X was
adjusted to retain a constant depth of oil/water The emulsion
flowed through the coalescer into reservoir Y until eventually
a constant depth of liquid was produced. At this stage, in
order to keep a steady state, liquid was drained out of
reservoir Y at the same rate as it entered reservoir X. The
variation in pressure head across the coalescer was 10.5 cm of
water at a constant flow of 9.2m3 per hour per square metre
of fabric.
Initial coalescence of oil droplets on the down-
stream side of the coalescer was very slow and consisted of
very small oil droplets. However, after 3 or 4 hours, coalescence
was much faster and the size of the oil droplets formed were
much larger and floated towards, and formed a layer on, the
, free surface of the liquid in reservoir Y.
At this stage, samples of the oil/water emulsion were
taken at about 30 minute intervals at a location O within
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` reservoir X immediately on the upstream side of the coalescer
and also at a location P within reservoir Y remote from the
downstream side of the coalescer after separation of the oil by
gravity had occured. With a hydraulic flow of 9.2m3 per hour
per square metre of fabric the liquid leaving the coalescer
was allowed to settle for 6 minutes before it arrived
~ at location P.
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106Z6'~7
With this hydraulic flow an average oil concentration
of 236 ppm ~at location Oj was reduced to an average of 0,9 ppm
(at location P)continuously over a 7 hour periodO
The efficiency of the coalescer was then studied with
various flow rates with equally good results.
EX~MPLE 2
Example 1 was repeated in entirety (apart from oil
concentration and flow rate) except that the coalescer was
! '~ produced by forming a three component lay-up by superLmposing
two pieces of Fabric B and one piece of Fabric A.
The following results were obtained:-
The pressure drop across the coalescer was 26 mm of
` water,
The oil concentration was reduced from 690 ppm(at location 0) to 17 ppm (at location P) over a four hour
period at a hydraulic flow of 9.8m3 per hour per square metre
' of fabric.
EXAMPLE 3
~, Example 1 was repeated in entirety (apart from oil
' 20 concentration and flow rate) except that the coalescer was
1! produced by forming a two component lay-up by superimposing
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two pieces of Fabric B.
The following results were obtained:-
The pressure drop across the coalescer was 3 cm of
water.
The oil concentration was reduced from 684 ppm
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(at location 0) to 43 ppm (at lo~ation P) over a four hourperiod at a hydraulic flow of 8m3 per hour per square metre of
fabric.
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1062627
EXAMPLE 4
Example 1 was repeated in entirety (apart frcm oil
concentration and flow rate) except that the coalescer was a
single piece of Fabric A, The following results were obtained:-
The pressure drop across the coalescer was 10 cm ofwater~ The oil concentration was reduced from 289 ppm (at
location O) to 36 ppm (at location P) over a four hour period
at a hydraulic flow of lO.Sm3 per hour per square metre of
fabric.
This shows that particularly efficient coalescers are
fibrous structures comprisin~ two or more superimposed area-
bonded fabrics followed by one or more point-bonded melded fabrics
as described herein.
;~ EXAMPLE 5
As a comparison, Example 1 was repeated except that
r~ the coalescer was produced by forming a four component lay-up by
superimposing three pieces of Fabric Atbefore it had been treated
with silane-coated silica particles as described in Ex~mple 1)
and one piece of Fabric B(before it had been treated with silane-
coated silica particles as described in Example 1).
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The pressure drop across the coalescer was now 14.5 cm
, of water. The oil concentration was reduced from 232 ppm (at
location 0) to 38 ppm over a four hour period(at location P)
at a hydraulic flow of 11.6m3per hour per square metre of fabric.
This shows that the coalescer used in Example 1 has a
much higher efficiency than the coalescer used in ~he present
Example.
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EXAMPLE 6 1062627
A coalescer was produced by superimposing two pieces
of Fabric B, This was fixed in position as a common wall
between reservoirs X and Y.
Effluent from the cleaning of road tankers used in
: the transport of mineral oils and vegetab~ oils with steam
and paraffin based detergents was passed into reservoir X,
Liquid was drained out of reservoir Y at the same rate as it
entered reservoir X, The variation in pressure head across
the coalescer wa.q a maximum of 20 centimetres of water at a
constant flow of 16 cubic metres per hour per square metre of
fabric.
: Samples of the 'oil'/water emulsion were taken at
regular intervals at a location O within reservoir X immediately
on the upstream side of the coalescer and also at a location P
~, within reservoir Y remote from the downstream side of the
coalescer after separation of the 'oil' by gravity had
occurred.
The results of separation achieved are given
.20 in the table below
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: "Oily"Oil Content ppm Oil Content ppm .
: Componentof Effluent after coalescence
;.' at location O at location P .
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. Palm Oil 153 88
'. Sunflower Oil/ 36 23 :
.. ~ Spindle/Crude Rape Oil
.~. Plasticiser 212 115 :
.~ Lead Naphthalate/
~ Mineral Oil 592 290
: 30 Chrome Liquor/
Mineral Oil 260 168
-- After extended use,the coalescer was successfully
-, cleaned with a jet of steam/hot water and after cleaning was
. re-used. -11-
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