An oil-water separation filter, which comprises (1) a porous material comprising a sintered polyethylene powder bonded to (2) a fibrous layer having a thickness of about 0.5 to about 5 mm and a porosity of about 70 to about 90% comprising fibers having a water content of about 0.4 to about 5%, a critical surface tension of about 25 to about 45 dyne/cm and a fiber diameter of about 5 to about 30 .mu. or a mixture of the fibers and fibers having a water content of about 8 to about 15% and a fiber diameter of 5 to about 30 .mu..

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates to a filter for separating and removing an oil 
contained in water. 
2. Description of the Prior Art: 
It is difficult to separate and remove an oil in water, especially an oil 
in the emulsified state, and in many cases water containing emulsified 
oils have been discharged into a sewer as such. Various attempts have been 
made to separate such an emulsified oil, for example, by standing, which 
comprises allowing water containing emulsified oils to stand for a long 
time in a storage tank, thereby separating the oils, by adsorbing, i.e., 
separating the oils using an oil-adsorbing layer, or by passing such water 
containing emulsified oils through a filter, thereby separating the oils 
as coarse particles. However, these methods suffer from various defects. 
For example, they require large apparatus or are of poor efficiency, or 
require high cost materials which are consumed in the process. 
Accordingly, factories handling machine oils, fuel oils, or vegetable oils 
have encountered substantial problems in preventing waste water containing 
oils from flowing into sewers. The disposal of oil-containing bilge water 
and cleaning water in ships has posed the same problem. 
SUMMARY OF THE INVENTION 
It is one object of this invention to provide a filter which permits 
continuous, efficient and simple separation and removal of oils from great 
quantities of water containing oils, thereby providing clear water having 
an extremely low oil content. 
According to this invention, there is provided a filter for separating oils 
from water comprising a first filter layer of a porous material produced 
from a sinterable polyethylene powder, or a mixture of such a polyethylene 
powder and a powder of a heat-resistant organic or inorganic material, 
which is bonded to a second filter layer comprising a fibrous layer. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
According to this invention, polyethylene powder having a viscosity average 
molecular weight of about 700,000 to about 4,000,000, or a mixture of 
polyethylene powder and an organic material such as a fluorine resin 
powder or a polyimide resin powder, or an inorganic material such as 
sintered clay, alumina, diatomaceous earth or activated carbon, which is 
used as a filler, is molded in a cylindrical or plate-like form, and 
sintered preferably at a temperature of about 220.degree. to about 
270.degree. C., preferably 230.degree. to 250.degree. C., to form a first 
filter layer having a predetermined pore diameter and porosity. 
Then, a fibrous layer, i.e., a second filter layer, comprising fibers 
having a water content of about 0.4 to about 5%, a critical surface 
tension of about 25 to about 45 dyne/cm and a fiber diameter of about 5 to 
about 30.mu., is bonded to the outer peripheral surface of a cylindrical 
first filter layer or to one of two surfaces having a maximum area of a 
plate-like first filter layer to form a filter of this invention. 
When water containing oils are caused to flow from the first filter layer 
of this filter towards the second filter layer, the oils contained in the 
water separate from the water as large droplets. When the fibrous layer is 
likely to be separated by the pressure of the flowing water to cause fiber 
migration, the fibrous layer is preferably covered with a wire gauze of a 
coarse mesh finished with a rust-proof resin, to thereby prevent such a 
defect. 
The function of the filter of this invention to separate oils from water is 
due to the first filter layer. However, this layer alone is insufficient, 
and in order to completely separate the oils, the filter must be of a 
composite structure consisting of a first filter layer and a second filter 
layer. When water containing oils pass through the fine pores of the 
sintered porous material as a first filter layer, the films covering the 
oil droplets are destroyed, and only the oils are retained and aggregated 
in the first filter layer due to the difference in wetting between the 
water and the oils toward the material of the first filter layer, whereby 
separation occurs. However, when the first filter layer is used alone, the 
separated oils come afloat along the surface of the first filter layer to 
cause a so-called froth or graping phenomenon (oil droplets can initially 
be seen in closely conteguous "grape-like" structures on the surface; they 
eventially come lose and float away from the surface), and the interface 
between the separated oils and the water becomes unstable. The 
characteristic feature of the filter of this invention is that the oil 
droplets separated in the first filter layer grow into large, stable oil 
droplets due to the second filter layer provided around or on top of the 
first filter layer, and then the oil droplets are released from the second 
filter layer and come afloat to form a stable interface between the oil 
and the water phase. 
The porous material used as a constituent of the first filter layer of this 
invention can suitably be made from ultra-high molecular weight 
polyethylene powder. From the viewpoint of low hydrophilicity, resistances 
to water, oils and chemicals, and strength, polyethylene powder having a 
viscosity average molecular weight of about 700,000 to about 4,000,000, a 
density of about 0.94 to about 0.97 g/cc, a melt index of not more than 
about 0.01 dg/min., a melting point of about 130.degree. to about 
138.degree. C. and a particle size of about 50 to about 200.mu. is 
suitable for use in this invention. 
Organic or inorganic powders can be added as a filler to the polyethylene 
powder in an amount of about 5 to about 50% by weight, to thereby form 
various sintered porous materials having a layer thickness of about 16 mm, 
a porosity of about 50 to about 70% and a pore diameter of about 10 to 
about 60.mu. in a cylindrical or plate-like form. In the above, the 
sintering is carried out at a temperature of about 220.degree. to about 
270.degree. C., preferably 230.degree. to 250.degree. C., for a period of 
about 70 to about 120 minutes, preferably 80 to 100 minutes, in air. The 
pore diameter and porosity of the sintered porous material formed are 
determined by the particle size distribution and amount of the filler 
used. 
Examples of organic powders used in this invention include 
tetrafluoroethylene powder having a specific gravity of about 2.25 to 
about 2.29, an apparent specific gravity of about 300 to about 500 g/l and 
a particle size of about 5.mu. (more than 50% of the particles); and 
polyimide powder having a specific gravity of about 1.4, an apparent 
specific gravity of about 400 g/l and a particle size of about 5.mu. (more 
than 50% of the particles). 
Examples of inorganic powders used in this invention include sintered clay 
having a specific gravity of about 2.5 to about 2.6 and a particle size of 
about 1 to about 5.mu.; activated carbon having a specific gravity of 
about 1.3 to about 1.5, a particle size of about 0.5 to about 2.mu. and a 
specific surface area of about 700 to about 1,300 m.sup.2 /g; diatomaceous 
earth having a specific gravity of about 1.98 to about 2.30 and a particle 
size of about 3 to about 40.mu.; alumina having a specific gravity of 
about 3.7 to about 3.9 and a particle size of about 30 to about 150.mu.; 
calcium carbonate having a specific gravity of about 2.7 to about 2.8 and 
a particle size of about 1 to about 50.mu.; magnesium carbonate having a 
specific gravity of about 2.8 to 2.85 and a particle size of about 40 to 
about 150.mu.; and magnesium hydroxide having a specific gravity of about 
2.38 to about 2.39 and a particle size of about 40 to about 75.mu.. 
Sodium chloride having a particle size of about 400.mu. can also be added 
to the polyethylene powder in an amount of about 40 to about 80% by 
weight, and sintered in a cylindrical or plate-like form at a temperature 
of about 220.degree. to about 270.degree. C., preferably 230.degree. to 
250.degree. C., for a period of about 70 to about 120 minutes, preferably 
80 to 100 minutes, in air, followed by washing with water to dissolve the 
sodium chloride, to thereby form various porous materials having a layer 
thickness of about 16 mm, a porosity of about 60 to about 80% and a pore 
diameter of about 50 to about 60.mu.. The porosity and pore diameter of 
the porous material formed are determined by the amount of sodium chloride 
added. 
Moreover, an inorganic foaming agent such as sodium bicarbonate having a 
particle size of about 30 to about 100.mu. or antimony bicarbonate having 
a particle size of about 50 to about 200.mu. can be added to the 
polyethylene powder in an amount of about 30 to about 70% by weight, and 
sintered in a cylindrical or plate-like form at a temperature of about 
220.degree. to about 270.degree. C., preferably 230.degree. to 250.degree. 
C., for a period of about 70 to about 120 minutes, preferably 80 to 100 
minutes, in air. Due to the presence of decomposed gases caused by the 
addition of the foaming agent during sintering, porous materials having a 
porosity of about 60 to about 80%, a pore diameter of about 50 to about 
150.mu. and a layer thickness of about 16 mm can be obtained. The porosity 
and pore diameter of the porous material formed are determined by the 
amount of the foaming agent added. 
It can, of course, be said that the thickness and form are not limited to 
the above, and can optionally be selected in this invention. 
The sintered porous material thus obtained is used as the first filter 
layer. The fibrous layer, i.e., the second layer, has a layer thickness of 
about 0.5 to about 5 mm and a porosity of about 70 to about 90% and 
comprises fibers (e.g., acrylate, polyamide, polyester, etc.) having a 
critical surface tension of about 25 to about 45 dyne/cm, a water content 
of about 0.4 to about 0.5% and a fiber diameter of about 5 to about 
30.mu., is bonded to the outer peripheral surface of the cylindrical first 
filter layer or to one of two surfaces having a maximum area of the 
plate-like first filter layer to form a filter of this invention. In this 
case, both ends of the cylindrical second filter layer, or one or two 
surfaces of the plate-like second filter layer are bonded to the porous 
material with an adhesive using, for example, end plates or seal frame. 
Mixed fibers comprising about 50% by weight of the fibers as described 
above and about 50% by weight of fibers (e.g., cotton, hemp, etc.) having 
a water content of not lower than about 8% (e.g., about 8 to about 15%) 
and a fiber diameter of about 5 to about 30.mu. can give a fibrous layer 
having a layer thickness of about 0.5 to about 5 mm and a porosity of 
about 80 to about 90% which is capable of being used as the second layer. 
The thus formed fibrous layer is bonded to the above-described porous 
material to form an effective filter for oil separation. 
Examples of adhesives used include an epoxy resin adhesive comprising 
material A and material B. As material A, a mixture of about 40 to about 
50% by weight of Epikote 828 (a registered trademark for a product of 
Shell International Chemicals Corp., which has an epoxy equivalent of 190 
to 200 and a molecular weight of 360 to 400) and about 50 to about 60% by 
weight of a filler is suitably used. As material B, a mixture of about 45 
to about 55% by weight of a polyamide and about 45 to 55% by weight of a 
filler is suitably used. A mixture of material A and material B in an 
amount of about 1:1 by weight is suitably used as the adhesive. 
The characteristic features of the filter can be optionally selected 
depending upon the viscosity and concentration of the oils separated. When 
an oil having a kinematic viscosity of not more than about 60 centisokes 
at 37.8.degree. C. (100.degree. F.) is separated from oil containing water 
in an oil concentration of not more than about 1%, a first filter layer 
having a pore diameter of about 15 to about 20.mu. and a porosity of about 
60 to about 70%, and a second filter layer having a layer thickness of 
about 1.5 to about 3 mm and a porosity of about 80 to about 85% comprising 
fibers having a critical surface tension of about 30 to about 35 dyne/cm, 
a water content of not lower than about 2% and a fiber diameter of about 
15 to about 20.mu., are suitably used. When an oil having a kinematic 
viscosity of not lower than about 60 centistokes at 37.8.degree. C. 
(100.degree. F.) is separated from oil containing water in an oil 
concentration of about 1 to about 5%, a first filter layer having a pore 
diameter of about 40 to about 60.mu. and a porosity of about 65 to about 
75%, and a second filter layer having a layer thickness of about 1.5 to 
about 3 mm and a porosity of about 80 to about 85% comprising about 50% of 
fibers having a water content of not lower than about 8% (e.g., about 8 to 
about 15%) and a fiber diameter of about 5 to about 20.mu. and about 50% 
of fibers having a water content of about 0.4%, a critical surface tension 
of about 40 to about 45 dyne/cm and a fiber diameter of about 10 to about 
15.mu., are suitably used. 
A filter paper treated with resins can also be used as the second filter 
layer. In this case, a filter paper having a pore diameter of about 50 to 
about 80.mu., a thickness of about 0.6 to about 1 mm, a porosity of about 
75 to about 85% and a Frazier air permeability of about 80 to about 110 
cc/cm.sup.2 /sec (at 1/2 in. H.sub.2 O below atmospheric; ASTM D-737-46), 
which mainly consists of cotton linter having a fiber diameter of about 25 
to about 30.mu., is impregnated with a 25% acetone solution of a mixture 
of about 91% by weight of an epoxy resin, such as Epikote 828 (a 
registered trademark for a product of Shell International Chemicals Corp., 
which has an epoxy equivalent of 190 to 200 and a molecular weight of 360 
to 400), and about 9% by weight of a curing agent, such as 
triethylenetetramine, and heated at about 130.degree. C. for about 5 hours 
in the air to form the second filter layer. 
Also, the same filter paper as described above can be impregnated with a 
20% acetone solution of a mixture of about 78% by weight of isophthalic 
acid polyester having a melting point of 80.degree. C. and a molecular 
weight of about 420 to about 700, about 20% by weight of a styrene monomer 
and about 2% by weight of benzoyl peroxide, and subjected to heating at 
about 150.degree. C. for about 5 hours in the air, to thereby form the 
second filter layer. 
Still further, the same filter paper as described above can be impregnated 
into a 10% acetone solution of polymethylmethacrylate having a degree of 
polymerization of about 1,000, and subjected to heating at about 
80.degree. C. for 3 hours in the air to form the second filter layer. 
In any case, the impregnation amount of the resin in the filter paper is 
limited to about 15 to about 20% based on the weight of the filter paper 
treated.

The following Example specifically illustrate the present invention without 
limiting the same. 
EXAMPLE 1 
Powder of ultra-high molecular weight polyethylene having a viscosity 
average molecular weight of about 1,000,000, an apparent specific gravity 
of 210 to 230 g/l, particle size of 50 to 200.mu., a density of 0.94 g/cc, 
a melt index of less than 0.01 dg/min. and a melting point of 130.degree. 
to 138.degree. C. was sintered in a hollow cylindrical form at a 
temperature of 230.degree. C. for a period of 90 minutes in the air to 
form a porous material having a layer thickness of 16 mm, a porosity of 
65% and a pore diameter of 40.mu.. A fibrous layer having a layer 
thickness of 2 mm and a porosity of 82% and comprising 50% of polyester 
fibers having a water content of 0.4%, a critical surface tension of 43 
dyne/cm, a specific gravity of 1.38 and a fiber diameter of 10.mu. and 50% 
of cotton fibers having a water content of 8%, a specific gravity of 1.54 
and a fiber diameter of 5 to 20.mu. in the form of a tube closed at one 
end was slipped onto the porous material, an imperforate end plate bonded 
to the closed end and an end plate with an opening was bonded to the open 
end of the tube the porous material so as to form an enclosing tube along 
the long axis thereof and the ends bonded to each other using end plates 
with an adhesive comprising a 1:1 mixture of Epikote 828 and a polyamide 
as hereinbefore defined as a curing agent to thereby form a second filter 
layer of the tubular filter. One of the ends of the tubular filter thus 
formed was closed and the other was left open (water/oil inlet). The 
amount of the water treated with this filter was 25 l/min. per 300 
cm.sup.2 of effective filtering area at a pressure loss of 0.14 
Kg/cm.sup.2. 
When oil-containing water prepared by emulsifying an oil having a kinematic 
viscosity of 30 to 60 centistokes at 37.8.degree. C. (100.degree. F.) (JIS 
K2219 First Class No. 1) in a concentration of about 1,000 ppm in the 
water was treated by the filter, and the remaining oil in the thus treated 
water was extracted with carbon tetrachloride, it was ascertained by 
non-dispersible infrared absorption method that the oil was separated to 
the extent that its concentration in the water became 20 ppm. 
EXAMPLE 2 
The same polyethylene powder as was used in Example 1 was mixed with 
polytetrafluoroethylene powder having an apparent specific gravity of 300 
to 500 g/l, a specific gravity of 2.3 and a particle size of 5.mu. (more 
than 50% of the particles) in ratio of 3:1 by weight, and sintered in a 
hollow cylindrical form at a temperature of 230.degree. C. for a period of 
90 minutes in the air to form a porous material having a layer thickness 
of 16 mm, a porosity of 64% and a pore diameter of 20.mu.. A fibrous layer 
having a layer thickness of 2 mm and a porosity of 85% and comprising 
fibers having a water content of 2%, a critical surface tension of 32 
dyne/cm, a specific gravity of 1.14 to 1.17 and a fiber diameter of 15 to 
80.mu. was slipped on the porous material so as to form an enclosing tube 
and both ends thereof bonded to each other as in Example 1 using the same 
adhesive as was used in Example 1 to thereby form a second filter layer of 
the tubular filter. One of the ends of the tubular filter thus formed was 
thus closed and the other was left open (water/oil inlet). The amount of 
water treated with the resulting filter was 20 l/min. per 300 cm.sup.2 of 
effective filtering area at a pressure loss of 0.14 Kg/cm.sup.2. 
When oil-containing water prepared by emulsifying an oil having a kinematic 
viscosity of 2 to 3 centistokes at room temperature (i.e., about 
20.degree.-30.degree. C.) (JIS K2203-1) in a concentration of about 4,500 
ppm in the water was treated by the filter, and the remaining oil in the 
thus treated water was extracted with carbon tetrachloride, it was 
ascertained by a non-dispersible infrared absorption method that the oil 
was separated to the extent that its concentration in the water became 3.5 
ppm. 
EXAMPLE 3 
The same polyethylene powder as was used in Example 1 was mixed with a 
polyimide powder having a specific gravity of 1.4, an apparent specific 
gravity of 400 g/l and a particle size of 5.mu. (more than 50% of the 
particles) in ratio of 3:1 by weight, and sintered in a hollow cylindrical 
form at a temperature of 230.degree. C. for a period of 90 minutes in the 
air to form a porous material having a layer thickness of 16 mm, a pore 
diameter of 15.mu. and a porosity of 60%. The same fibrous layer as was 
used in Example 2 was bonded to the porous material as in Example 2 as the 
second filter layer to form a filter. One of the ends of the tubular 
filter thus formed was closed and the other was left open (water/oil 
inlet). The amount of water treated with the resulting filter was 20 
l/min. per 300 cm.sup.2 of effective filtering area at a pressure loss of 
0.14 Kg/cm.sup.2. 
When oil-containing water prepared by emulsifying an oil having a kinematic 
viscosity of 2 to 3 centistokes at room temperature (JIS K2203-1) in a 
concentration of about 3,000 ppm in the water was treated by the filter, 
and the remaining oil in the thus treated water was extracted with carbon 
tetrachloride, it was ascertained by a non-dispersible infrared absorption 
method that the oil was separated to the extent that its concentration in 
the water became 5.6 ppm. 
EXAMPLE 4 
The same polyethylene powder as was used in Example 1 was mixed with 
diatomaceous earth having a specific gravity of 2.1, an apparent specific 
gravity of 250 g/l and a particle size of 3 to 40.mu. in ratio of 3:1 by 
weight, and sintered in a hollow cylindrical form at a temperature of 
230.degree. C. for a period of 90 minutes in the air to form a porous 
material having a layer thickness of 16 mm, a pore diameter of 15.mu. and 
a porosity of 67%. The same fibrous layer as was used in Example 2 was 
bonded to the porous material as in Example 2 as the second filter layer 
to form a filter. One of the ends of the tubular filter thus formed was 
closed and the other was left open (water/oil inlet). The amount of water 
treated with the filter thus formed was 25 l/min. per 300 cm.sup.2 of 
effective filtering area at a pressure loss of 0.14 Kg/cm.sup. 2. 
When oil-containing water prepared by emulsifying an oil having a kinematic 
viscosity of 30 to 60 centistokes at 37.8.degree. C. (100.degree. F.) (JIS 
K2219 First Class No. 1) in a concentration of about 5,000 ppm in the 
water was treated by the filter, and the remaining oil in the thus treated 
water was extracted with carbon tetrachloride, it was ascertained by a 
non-dispersible infrared absorption method that the oil was separated to 
the extent that its concentration in the water became 3.6 ppm. 
EXAMPLE 5 
The same polyethylene powder as was used in Example 1 was mixed with sodium 
chloride having a specific gravity of 2.16, an apparent specific gravity 
of 1,020 g/l and a particle size of 400.mu. (more than 50% of the 
particles) in ratio of 2:3 by weight, and sintered in a hollow cylindrical 
form at a temperature of 230.degree. C. for a period of 90 minutes in the 
air, followed by washing with water to dissolve the sodium chloride 
thereby forming a porous material having a layer thickness of 16 mm, a 
porosity of 70% and a pore diameter of 50.mu.. The same fibrous layer as 
was used in Example 1 was bonded to the porous material as in Example 1 as 
the second filter layer to form a filter. One of the ends of the tubular 
filter thus formed was closed and the other was left open (water/oil 
inlet). The amount of water treated with the resulting filter was 30 
l/min. per 300 cm.sup.2 of effective filtering area at a pressure loss of 
0.14 Kg/cm.sup.2. 
When oil-containing water prepared by emulsifying an oil having a kinematic 
viscosity of 250 centistokes at 37.8.degree. C. (100.degree. F.) (JIS 
K2205 Third Class No. 2) in a concentration of about 20,000 ppm in the 
water was treated by the filter and the remaining oil in the thus treated 
water was extracted with carbon tetrachloride, it was ascertained by a 
non-dispersible infrared absorption method that the oil was separated to 
the extent that its concentration in the water became 80 ppm. 
EXAMPLE 6 
A filter paper having a pore diameter of 50.mu., a thickness of 0.7 mm, a 
porosity of 80% and a Frazier air permeability of 94 cc/cm.sup.2 /sec (at 
1/2 in. H.sub.2 O below atmospheric; ASTM D-737-46), which mainly 
consisted of cotton linter having a fiber diameter of 25 to 30.mu., was 
impregnated with a 25% acetone solution of a mixture of 91% by weight of 
Epikote 828 as hereinbefore defined and 9% by weight of 
triethylenetetramine used as a curing agent and heated at 130.degree. C. 
for 5 hours in the air. The thus treated filter paper was shaped into a 
cylindrical form, and fitted on the same cylindrical porous material 
comprising a polyethylene-diatomaceous earth mixed powder as was prepared 
in Example 4. Both ends thereof were then bonded to each other using end 
plates as in Example 1 using the same adhesive as was used in Example 1 
following the procedure of Example 1 to form a filter. One of the ends of 
the tubular filter thus formed was closed and the other was left open 
(water/oil inlet). 
When oil-containing water prepared by emulsifying an oil having a kinematic 
viscosity of 1.5 to 1.7 centistokes at the 37.8.degree. C. (100.degree. 
F.) (JIS K2203-1) in a concentration of about 3,000 ppm in water was 
treated by the thus formed filter, and the remaining oil in the thus 
treated water was extraced with carbon tetrachloride, it was ascertained 
by a non-dispersible infrared absorption method that the oil was separated 
to the extent that its concentration in the water became 4 ppm. 
EXAMPLE 7 
The same filter paper as was used in Example 6 was impregnated with a 20% 
acetone solution of a mixture comprising 78% by weight of isophthalic acid 
polyester having a melting point of 80.degree. C. and a molecular weight 
of 420 to 700, 20% by weight of styrene monomer and 2% by weight of benzyl 
peroxide, and heated at 150.degree. C. for 5 hours in the air. The thus 
treated filter paper was then shaped into a hollow sylindrical form, and 
fitted on the same cylindrical porous material comprising a 
polyethylene-diatomaceous earth mixed powder as was prepared in Example 4. 
Both ends thereof were then bonded to each other using end plates with the 
same adhesive as was used in Example 1 following the procedure of Example 
to form a filter. One of the ends of the tubular filter thus formed was 
closed and the other was left open (water/oil inlet). 
When oil-containing water prepared by emulsifying an oil having a kinematic 
viscosity of 2 to 3 centistokes at room temperature (JIS K2203-1) in a 
concentration of about 5,000 ppm in the water was treated by the thus 
formed filter, and the remaining oil in the thus treated water was 
extracted with carbon tetrachloride, it was ascertained by a 
non-dispersible infrared absorption method that the oil was separated to 
the extent that its concentration in the water became 5.5 ppm. 
EXAMPLE 8 
The same filter paper as was used in Example 6 was impregnated with a 10% 
acetone solution of polymethylmethacrylate having a degree of 
polymerization of about 1,000, and heated at 80.degree. C. for 3 hours in 
the air. The thus treated filter paper was shaped into a hollow 
cylindrical form, and fitted on the same porous material comprising a 
polyethylene-diatomaceous earth mixed powder as was prepared in Example 4. 
Both ends thereof were then bonded to each other using end plates with the 
same adhesive as was used in Example 1 to form a filter following the 
procedure of that Example. One of the ends of the tubular filter thus 
formed was closed and the other was left open (water/oil inlet). 
When oil-containing water prepared by emulsifying an oil having a kinematic 
viscosity of 30 to 60 centistokes at 37.8.degree. C. (100.degree. F.) (JIS 
K2219 First Class No. 1) in a concentration of about 2,500 ppm in the 
water was treated by the thus formed filter, and the remaining oil in the 
thus treated water was extracted with carbon tetrachloride, it was 
ascertained by a non-dispersible infrared absorption method that the oil 
was separated to the extent that its concentration in the water became 2.0 
ppm. 
EXAMPLE 9 
A porous fluorine resin sheet comprising polytetrafluoroethylene and having 
a thickness of 1 mm and a pore diameter of 20.mu. was tightly wrapped 
around a stainless steel punching plate having a thickness of 0.8 mm and a 
porosity of 58% which had been formed into a hollow cylinder with a 
diameter of 58 mm and a length of 250 mm so that it formed a fluorine 
resin layer of a thickness of 5 mm. Then, a punching plate of the same 
quality formed into a cylinder with a diameter of 70 mm and a length of 
250 mm was fitted as a supporting member on the resulting assembly to form 
a first filter layer. Further, the same fibrous layer as was prepared in 
Example 2 was fitted on the first filter layer as a second layer, both 
ends of which were then bonded to each other using end plates with the 
same adhesive as was used in Example 1 (and following the procedure of 
that Example) to form a filter. One of the ends of the tubular filter this 
formed was closed and the other was left open (water/oil inlet). The 
amount of water treated with the thus formed filter was 15 l/min. per 300 
cm.sup.2 of effective filtering area at a pressure loss of 0.14 
Kg/cm.sup.2. 
When oil-containing water prepared by emulsifying an oil having a kinematic 
viscosity of 2 to 3 centistokes at room temperature (JIS K2203-1) at a 
concentration of about 1,500 ppm was treated by the filter, and the 
remaining oil in the thus treated water was extracted with carbon 
tetrachloride, it was ascertained by a non-dispersible infrared absorption 
method that the oil was separated to the extent that its concentration in 
the water became 3.6 ppm. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.