Note: Descriptions are shown in the official language in which they were submitted.
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The present invention concerns the removal of oil
from an oil in water emulsion. '~ ~,
In our co-pending Canadian application Serial No.
211,876 filed on 11th March, 1975, we have described methods
for removing oil from mixtures of oil a~d water. In part:icular
we have described how emulsified oil droplets can be caused to
coalesce by passing an ~il in water emulsion through a fibrous
structure comprising fibres having particles o~ their surface
wh,ich exhibit olèophilic and hydrophobic properties. The oil
10 droplets coalesce into much larger droplets which can be removed ,~
by gravimetric separation i.e. flotation of the oil from the -~
emulsion in a chamber located downstream of the fibrous structure.
Whilst the fibrous structures described in Canadian
patent application Serial No. 211,876 have been found to be par~
ticularly success~ul in achieving coalescence o unstable primary
emulsions which are characterised by an oil droplet size of the ~`
order o~ 100 microns, it has not been as successful in achieving ' ,;~
coalescence of secondary emulsions consisting of oi',', droplets of ~ ','
. . . .
' submicron size. ; ';
According to the presen~ invention we provide a method
for the removal of oil from an oil in water emulsion which com-
prises contacting the emulsion with a fibrous structure compris-
ing inorganic fibres which, in the emulsion, have a positive
zeta potential, and removing the coalesced oil droplets so formed.
; It is thought that the oil droplets being negatively
charged, are attracted to the surface of the individual inorganic
fibres in the fibrous structure and coalesce formin~ larger drop-
lets which detach themselves from the fibrous structure. The
laxger droplets so formed can then conveniently be separated
from the oil/water emulsion by allowin~ the droplets to float to
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the sur~ace to form a layer of oil which can be removed.
Though, in the method o the invention, the emulsion
may merely contact the surface of the fibrous structure, as
would be the case if the emulsions were passed over the surface
of the ibrous structure, as, for example, when the fibrous
structure constitutes one or more surfaces o a parallel plate
~saparator, we pre~er, in order to produce ef~ective coalescence
o the oil, to pass the emulsion through the fibrous structure.
Though the fibrous structure may comprise any inorganic
10 fibres which acquire a positive æeta potential when immersed in ~-
the particular oil in water emulsion, particularly suitable fibres
are those made rom aIumina.
When immersed in oil/water emulsions at various pH
values, alumina fibres acquire a zeta potential in the range 50
millivolts (at pH 4) to 30 millivolts ~at pH 7) to 0 millivolts
(at pH 8.5).
It will be realised, therefore,that fibrous structures
composed of alumina fibres are most useful in those emulsions
having a~pH less than 8.5.
Nevertheless, as it is usual for the pH of the emulsion
to be approximately 7, we preer to use those alumina fibres and
zirconia fibres sold by Imperial Chemical Industries Limited
under the Trade Mark 'Saffil' because 'Safil' fibres are micro-
porous and so have a particularly large surface area which is
itself conducive to the coalescence of oil droplets within the
emulsion. They can be produced with surace area as measured
by BET/nitrogen adsorption within the range 100 to 150 m /g.
- In contrast the surace area calcu~ated for a s oth f;bre such
as glass of diameter 3 microns is only 0.48 m2/g.
In general, the average diameter and diameter distri-
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bution o the ~ibres are important in providing desirea bulk
properties in the ibre mass. Fine fibre diameters and rela-
tively narrow diameter distributions are preferred. An average
fibre diameter of 0.5 to 5 microns is especially preferred; a
diameter distribution which ensures that the fibre mass contains
not greater than 30% by number of fibres o greater diameter
than 5 microns, for example not greater than 20% by number of
fibres of greater diameter than 5 microns is also especially
preferred. Relative freedom from shot, that is the substantial
absence, for example less than 1% by weight, of material o~ a
non-fibrous nature is a desirable property of fibres for use in
the invention, as the prasence of shot tends to reduce the uni-
formity of flow of rluid through the fibrous mass. Fibres of
alumina prepared as disclosed in United Kindgom patent Speci-
fication No. 1360197 and in our copending ~anadian patent
application Serial No. 166347 iled on 15th March, 1973 are
especially useful as they have the desired properties.
; The fibrous structure used in the method of the in-
vention may be a woven or non-woven fabric formed from the
- 20 inorganic fibres. Alternatively the fibrous structure may be
`~ loosely packed chopped fibres in which case it may be necessary
to retain the fibrous structure between open-weave or open-
mesh sheets.
Included in this fibrous structure may be other fibres
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such as inorganic fibres, for example calcium or aluminium
silicate fibresr and vitreous aluminosilicate fibres; natural
fibres such as cotton or rayon; synthetic fibres such as fibres
of a polyolefine or a polyester.
The opposed faces of the fibrous structure are usually
substantially flat and in this case the fibrous structure usually
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comprises a wall of a chamber which contains the emulsion to be -
treated. If a difference in pressure head is maintai~ed across
the ~ibrous structure then the emulsion will flow continuously
through the fibrous structure. Alternatively the fibrous struc- `~
ture ma~ be moulded to some shape such as a tube. A particularly ;
desirable shape is a tube which is closed at one end, i.e. ~;~
resembling a large test-tube, in which case the emul~ion can be
passed into the closed tube and if a suitable diference in pressure 3
head is maintained across the fibrous structure, the èmulsion
10 passes continuously through the walls of the tube and coalescence
of the oil droplet particles occurs.
It is understood that the fibrous structures described ~`
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herein are particularly useul in treating secondary emulsions
and so, if the mixture to be treated contains both primary and
secondary emulsions then the mixture can be effectively treated
in a number of stag_s viz (1) contacting the mixture of primary
-~ and secondary emulsions with a fibrous structure as described in -
Canadian patent application Serial No. 211,876 or some other
oleophilic and hydrophobic fibrous structure whence coalescence
20 of the primary emulsion occurs, (2)~allowing the coalesced oil
particles to float to the surface of the mixture to form a
layer of oil and removing this, ~3) contacting the essentially
secondary emulsion with a fibrous structure comprising inorganic
ibres which, when immersed in the emulsion, acquire a positive
zeta potential, and (4) allowing the coalesced oil particles to
float to the surface of the water to form a layer of oil and
removin~ this. In certain cases, however, it might be necessary
to repeat stage (1) and (2) before stage ~3) is carried out.
Furthermore it may be~desirable to repeat stages (3) and (4) in
30 order to reduce the oil concentration to an acceptable level.
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Also in stages (1) and (3) it is pre~erred that the emulsion
is passed through the ~ibrous structure.
In certain cases the oil droplets may not coalesce
to a suf~iciently large size for them to separate, by flotation,
from the emulsion. Under these oirc~umstances it may be neces-
sary to provide one or more other coalescexs such as those
described in Canadian patent application Serial No. 211876
downstream of the inorganic fibrous structure in order to achieve
a satisactory separation of oil from the emulsion~ Though
these other coalescers may be spaced from the inorganic ibrous
structure we prefer to merely form~a lay-up by superimposing a -
` sheet of the inorganic ~ibrous structure on one or more sheets
having a fibrous structure comprising ibres having particles on
their surface which exhibit olephilic and hydrophobic properties.
, i :
A suitable arrangement is a three component lay-up comprising
an inorganic fibrous structure followed by an area-bonded melded
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fabric followed by a point-bonded~melded fabric, the latter two
fab~ics havlng~a fibrous structure comprising fibres having par-
ticles on their surface which exhibit oleophilic and hydrophabic
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~; 20 properties. ~ -
The invention will now be described with reference to
the following Examples: ~-
Example 1
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An area-bonded, melded fabric of 137 g per square metre,
~` produced from staple ibres of oriented, i.e. drawn, sheathJcore
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heterofilaments in which the core ~50~ by weight of total weight
of filament~ was polyethylene terephthalate of melting point 257C
and the sheath was a copolymer of polyethylene terephthalate ana
polyethylene adipate (85:15 mole ratio) of melting point 220C,
was passed through a 2~ dispersion of silane-coated silica
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particles ~Silanox* 101 manufactured by Cabot Coxporation;
primary particle size 7 millimicrons; BET surface area 225 m /g~
in trichloroethylene. The dried fabric was held at constant
area on a pin stenter frame while being heated at 217C for ten
minutes, and finally rinsed with water to remove loosely adhering
particles. Drops o~ water placed on the dried fa~ric had a mean
` contact angle of 155C.
With a typical mineral oil in water emulsion having an
oil concentration o 684 ppm and pH 7~ the oil concentration can
- be r~duced to 43 ppm by a single pass through a coalescer pro-
duced by forming a two component lay-up b~ superimposing two
pieces of the treated ~abric. Further passes through a similar
coalescer only serve to reduce the oil concentration in the
liquid phase by a small proportion indicating that the emulsion . `~
is effectively a secondary emulsion. :~
If, however, the secondary emulsion at pH 7 is passed .
through a fibrous structure comprising chopped zirconia fibres
('Saffil') of mean diameter 3 microns.sandwiched between op~n-
mesh 7Netlon'* sheets further coalescence occurs and, after
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allowing 5 minutes settlement during which coalesced oil drop-
Iets float to the surface and ~orm a layer of oil which can be
easily removed, the oil concentration in the liquid phase is
reduced to 21 ppm at flows of 8 m3 per hour per sq~are metre oi
fabric.
Example 2
A point-bonded, melded ~abric of similar construction
to that described in Example 1 was treated in a similar manner
to that described in Example 1.
. Even though in Example 1 the use of a fibrous structure ~.
comprising chopped zirconia flbres served tv reduce the
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concentration in the secondary emulsion by a considerable
amount nevertheless it was apparent that a large number of the
coalesced oil droplets were of insufficient size for them to
float to the surface of the emulsion stream.
In the present example, Example 1 was repeated in
entirety except that the secondary emulsion had a concentration
of 5 ppm, the hydraulic 10w was greater than 10 m3 per hour per
square metre o fabric and the chopped zirconia fibrous structure
was replaced by a fibrous structure comprising a lay-up of ~:
three superimposed sheets consisting of a chopped alumina fibre ~,'
fibrous structure ~'Safil' of mean diameter 3 microns sand-
wiched between open-mesh 'Netlon'*~sheets) followed by a treated
area-bonded me~ded fabric (a~s in Example 1) followed by a
treated point-bonded mel'ded fabric (described above in this .
Example~
In this case considerable coalescence of oil droplets
occured and they were of sufficient size to float to the surface
of the emulsion to form a layer which could be removed by a '~
floating take-off arm. The concentration of the oil in the
residual emulsion was now only 0.2 ppm after allowing settle-' ~
ment for 6 minutes. ~` ' .
Example 3
Example 2 was rèpeated in entirety except that the
secondary oil emulsion had a concentration of 9 ppm and the ~-
hydraulic flow was 9.2 m3 per hour per square metre of fabric~ . ;,
The concentration in the residual oi} was 3 ppm after allowing
settlement for 6 minutes~
Example 4
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',~ UsPd motor car oil (Duckhams 30/50 at 3,500 miles~
was dispersed in tap water (ph = 7) using a high speed mixer
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to ~orm an oil in water emulsion~ The emulsion, ater settling, -
con~ained 1051 ppm of oil and was stable for several hours as
assessed by turbidity.
About 5Q mls of the emulsion was passed through a pad
of loosely chopped fibres held between the flanges of a pair of
: flanged ~lass tubes using rubber packing pieces to prevent end
compressing and edge leakage.
The time taken for the emulsion to fill a 10 ml mea-
suring cylinder provided the 1Ow rate thrvugh the fibrous pad,
10 A sample was taken and the turbidity measured immediately on a : ;
colorimeter which had previously been calibrated against the
emulsion~ at various dilutions covering the range 100% to 0.01~.
The oil content of the emulsion was obtained by progressively :~
e~tracting the oil with 60 - 80~ petroleum ether, combining the
extracts and evaporating at 100C.
Comparative tests were carried out with fibrous pads
made from glass fibre ~Owens-Corning* FM 004)~ which has a
negative zeta potential, and alumina fibxes (~Saf~ which
have a positive zeta potential when immersed in t~e oil in
2C water dispersion (ph = 7). The individual glass ibres and
alumina fibres used in the fibrous pads had similar~ but not
identical, diameters.
The results obtained are set out in the followiny
table:
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Fibre Weight of Flow Rate Oil ir Water Removal
Sample3 2 Before After of Oil
(grams) m /hr/m . 'ppm ' ppm , , ,% , ~ :~
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Glass 0.183 7.2 860 360 58.3
0.410~ 7.2 860 247 71.4 ' ~"'
0.6054 6.0 8~0 215 75.1
Alumina 0.2652 10.3 860 265 69.4 ;
0.53~2 7.2 ~60 196 77.2 :
: 1.4342 7.2 860 25 ~ 97.2
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~: 10 From the results it was apparent that alumina provided
a very high remo~al of oil~ down to 25 ppm at 6 m3/hr/m~. In '`''!
contrast, glass fibre, which has a negative zeta,potential,
reduced the oil level to only 170 ppm even at a much lower flow
rate o 3 m3/hr/m .
~, Example 5 ,
An oil/water emulsion at a given pH was passed through
a fibrous structure comprising chopped alumina fibres (Saffil)~ `
of mean ~iameter 3 microns sandwiched between two layers of an
area bonded melded fabric (as described in Example 1). Coales- -
-20 cence of the oil droplets occurred~ After allowing 5 minutes
for settlement, the coalesced oil droplets floated to the sur-
face and were skimmed from the surface~ The hydraulic flow
through the fabric was 10 m3/hr/m2 fabric cross sectional area~ -
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~,, The pH of the emulsion was varied in the range 2.5 to 10 and
the following results were obtained.
: inlet oil outlet oil
; p~ concentration concentration
, ppm , ppm, :i
' 2.5 15~6 2 , ' '
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.,"' 7.0 3~98 34 ,~,
~'"' 30 7.0 2203 116
~'' 10.0 1290 110
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The results indicate that alumina fibres are less
effective as an oil coalescer in alkaline solutions i.~. when
the fibrous sur~ace no longer exhibits a positive zeta potential.
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