Note: Descriptions are shown in the official language in which they were submitted.
CA 02898815 2015-07-27
A PREPARATION METHOD OF AN OIL-ABSORBING HOLLOW FIBER POROUS
MEMBRANE
BACKGROUND OF THE INVENTION
[0001] Technical Field
[0002] The invention relates to a technique for preparing a functional hollow
fiber
membrane, and specifically in the preparation method of an oil-absorbing
hollow fiber
porous membrane.
[0003] 2. Description of Related Art
[0004] In recent years, with increasing problems of water resource (such as
river, ocean,
etc.) and environment pollutions caused by oily organic compounds and its
organic waste
water, waste fluids and various accidents like oil tanker or oil leakages,
traditional
oil-absorbing materials (e.g. clay, paper pulp, wood, cotton, etc.) cannot
meet the needs of
oily waste water recycling and environmental management because of their low
oil
adsorption capacity, poor oil-water selectivity and unsatisfactory oil
retaining ability.
[0005] Among various processing methods for oil pollutants, oil-absorbing
fiber has
been widely used because of its large specific surface area, fast oil
adsorption rate, high
efficiency, easy oil recycling and other advantages. Xiao et al. fabricated
oil-absorbing
copolymethacrylate fiber (CN 200710059780.7; CN 200410019338.8). Liu et al.
prepared
superfine oil-absorbing fiber by using the electrospinning technology (CN
200710043566.2). However, these oil-absorbing fibers can only swell and absorb
oil
through the void between the fibers or polymer crosslinked networks. When the
oil
adsorption capacity reached at saturation, the adsorption function of the oil-
absorbing
fiber would be depleted and the fiber could not be continuously used, however,
the
oil-absorbing material needs to be desorbed and recycled. In fact, the desired
oil-absorbing
material has low service efficiency and high disposal cost, and it is
difficult to meet the
CA 02898815 2015-07-27
should meet the needs of continuous treatment, fast and efficient organic
waste water
disposal, pollution due to large area oil spill on water surface,
environmental protection
and the like.
[0006] The graphene-based porous polymer oil-absorbing material is a novel
oil-absorbing material. In 2011, D. Zha et al. obtained superhydrophobic
oleophylic
PVDF/graphene porous material. The preparation process is as follows: firstly,
the
PVDF/graphene gel was formed by diffusion of methanol or water into
PVDF/graphene
suspension in N,N-dimethylformamide (DMF), and then replaced DMF in the gel
with
water, and followed by freeze-drying for the final product. (Zha D, Mei S.
Wang Z, et al.
Superhydrophobic polyvinylidene fluoride/graphene porous materials. Carbon,
2011,
49(15): 5166-5172.); in 2012, D. D. Nguyen et al. immersed a melamine sponge
into an
ethyl alcohol dispersion liquid of the graphene to obtain a graphene-coated
sponge, and
the graphene-coated sponge endured surface treatment by polydimethylsiloxane
to prepare
a superhydrophobic oleophylic sponge-based graphene material (Nguyen D D, Tai
N H,
Lee S B, et al.. Superhydrophobic and superoleophilic properties of graphene-
based
sponges fabricated using a facile dip coating method. Energy & Environmental
Science,
2012, 5(7): 7908-7912.). The above-mentioned material has a strong absorption
ability for
oily organic compounds, showing the maximum adsorption capacity for
trichloromethane
up to 165 times its own weight. In 2013, Liu et al. immersed a polyurethane
foam into the
dispersion liquid of the graphene oxide, adjusted the pH of the dispersion
liquid, and
reduced the graphene oxide by using hydrazine to prepare a superhydrophobic
oleophylic
sponge-based graphene oil-absorbing material (Yue Liu, Junkui Ma, Tao Wu, et
al..
Cost-effective reduced graphene oxide-coated polyurethane sponge as a highly
efficient
and reusable oil-absorbent. ACS Applied materials & interfaces, 2013,
5(20):10018-10026.). The maximum adsorption capacity of the as-prepared
material for
trichloromethane reaches 160 g/g. The above-mentioned polymer-based graphene
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CA 02898815 2015-07-27
oil-absorbing materials have attracted people's attention because of its good
oil and water
selectivity and high oil adsorption capacity far exceeding that of the
conventional intrinsic
synthetic oil-absorbing resin material. However, the oil adsorption process of
these
oil-absorbing materials still is intermittent operation, which cannot realize
continuous
efficient adsorption and separation of the oil-water system; as for they are
limited in the
industrial scale-up.
BRIEF SUMMARY OF THE INVENTION
[0007] For the shortage of the existing oil-absorbing material, the technical
problem to
be solved by the invention is to provide a preparation method of an oil-
absorbing hollow
fiber porous membrane. Starting from oil adsorption of the material, the
preparation
method is implemented by taking superhydrophobic oleophylic graphene as a
surface
adsorption layer and taking an oleophylic (non-swelling) hollow polymer fiber
porous
membrane as a matrix layer. The oil-absorbing hollow fiber porous membrane
combines
oil absorbents with the benefits of oil adsorption performance and oil-water
separation
function, and further the membrane can achieve the characteristics of
continuous oil
adsorption and water-repellency and continuous oil-water separation.
Meanwhile, the
membrane can be processed and formed into products of various types with
simple
process and low cost, so that it satisfies the requirement of industrial
applicability.
[0008] The technical solution of the invention for solving the technical
problem is to
design a preparation method of an oil-absorbing hollow fiber porous membrane.
The
preparation method is implemented by taking graphene as a surface adsorption
layer and
taking a hollow fiber porous membrane as a matrix layer through the following
preparation process:
[0009] (1). Preparation graphene dispersion liquid: Mixing 0.1-1g of graphene
with
200-1000 ml of dispersant, and carrying out ultrasonic dispersion for 10-50
min to prepare
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the graphene dispersion liquid, wherein the graphene has a thickness of less
than 10 nm
and a diameter of 0.1-5 1.1m; and the dispersant is one of absolute ethyl
alcohol, N-methyl
pyrrolidone, tetrahydrofuran, dimethylformamide or dimethylacetamide.
[0010] (2). Preparation of an oil-absorbing hollow fiber porous membrane:
First,
preparing a polymer hollow fiber porous membrane into module, immersing the
module
into the graphene dispersion liquid prepared in step (1), and carrying out
dead-end
pumping filtration under a negative pressure of 0.02-0.08 MPa for 5-30 min.
Then the
membrane is naturally dried in the air until the excess graphene on the
surface of the
hollow fiber porous membrane falls off, and put it in a vacuum oven under a
negative
pressure of 0.1 MPa for drying at a room temperature for 6-12 h, wherein the
polymer
hollow fiber porous membrane is polyvinyl chloride hollow fiber membrane,
polyvinylidene fluoride hollow fiber membrane, polypropylene hollow fiber
membrane or
polyacrylonitrile filament braided hollow tube; and the temperature of the
graphene
dispersion liquid is 20-30 C.
[0011] (3). Enhancement of the interface bonding strength between the graphene
and
the hollow fiber porous membrane: Enhancing the interface bonding strength
between the
graphene and the hollow fiber porous membrane by using one of the following
two
processing methods, alternately: 1) a solvent processing method: first,
prepare 20-100
wt% of an aqueous solution of a solvent, then immerse the oil-absorbing hollow
fiber
porous membrane prepared in step (2) into the aqueous solution of designated
solvent for
1-20 s, and quickly take the membrane out and put it in a coagulation bath for
solidifying,
yielding the oil-absorbing hollow fiber porous membrane, wherein the solvent
is one of
dimethylformamide, dimethylacetamide, dimethyl sulfoxide or dimethylbenzene;
and the
coagulation bath is water; 2) A dilute solution processing method: firstly,
preparing a
dilute solution, then immerse the oil-absorbing hollow fiber porous membrane
prepared in
step (2) into the dilute solution, carry out pumping filtration under a
negative pressure of
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0.02-0.08 MPa for 3-20 s, and quickly take the membrane out and put it in a
coagulation
bath for solidification. This yields the oil-absorbing hollow fiber porous
membrane,
wherein the dilute solution is composed of polymer material, additives and
solvents, as
each constituent percentage of total quantity is 0.5-6wt%, 0-12wt% and 82-
99wt%,
respectively. The polymer is polyvinyl chloride, polyvinylidene fluoride,
polypropylene or
polyacrylonitrile; the additive is one of the distilled water, anhydrous
lithium chloride,
polyvinylpyrrolidone or polyethylene glycol; the solvent one of is
dimethylformamide,
dimethylacetamide, tetrahydrofuran or decahydronaphthalene; and the medium of
the
coagulation bath is the aqueous solution of the solvent.
[0012] The invention proposed for the first time the design concept for
realizing oil
adsorption and separation function simultaneously by using the special form of
the hollow
fiber porous membrane. Compared to the prior art, the oil-absorbing hollow
fiber porous
membrane of the invention has continuous oil adsorption and separation
function, large
specific surface area for oil adsorption, fast oil adsorption rate, high
efficiency and easy oil
recycle. The oil-absorbing hollow fiber porous membrane of the invention can
be
processed into products of various types and purposes as you required. While
treating
water polluted by oily organic matters, the porous membrane can float on the
surface of
water, and oil adsorption occurs at the oil-water interface, which broadens
the application
range and area. Moreover, the invention has simple process, low cost, easy
industrial
implementation and good economic and social benefit prospect.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0013] Fig. 1 is the structural schematic diagram of a continuous test device
of the
oil-absorbing hollow fiber porous membrane prepared by a preparation method of
the
invention.
CA 02898815 2015-07-27
DETAILED DESCRIPTION OF THE INVENTION
[0014] Hereinafter, the invention is described in further detail in
conjunction with
examples and drawing.
[0015] The preparation method (hereinafter referred to as preparation method)
of an
oil-absorbing hollow fiber porous membrane designed in the invention is
implemented
by taking graphene as a surface adsorption layer and taking a hollow fiber
porous
membrane as a matrix layer through the following preparation process:
[0016] (1) Preparation of a graphene dispersion liquid: Mixing 0.1-1g of
graphene with
200-1000m1 of a dispersant, and carrying out ultrasonic dispersion for 10-50
min to form
the graphene dispersion liquid, wherein the graphene has a thickness of less
than 10 nm
and a diameter of 0.1-5 p.m; and the dispersant is one of absolute ethyl
alcohol, N-methyl
pyrrolidone, tetrahydrofuran, dimethylformamide or dimethylacetamide;
[0017] (2) Preparation of an oil-absorbing hollow fiber porous membrane:
First,
preparing a polymer hollow fiber porous membrane into module, and immersing
the
module into the graphene dispersion liquid prepared in step (1); pumping
filtration from a
dead-end under a negative pressure of 0.02-0.08 MPa for 5-30 min. Then the
membrane is
naturally dried in the air until excess graphene on the surface of the hollow
fiber porous
membrane falls off, putting it in a vacuum oven under a negative pressure of
0.1 MPa for
drying at a room-temperature for 6-12 h, wherein the temperature of the
graphene
dispersion liquid is 20-30 C;
[0018] (3) Enhancement of the interface bonding strength between the graphene
and the
hollow fiber porous membrane: Enhancing the interface bonding strength between
the
graphene and the hollow fiber porous (based) membrane by using one of two
processing
methods, alternately: 1) a solvent processing: preparing 20-100 wt% of an
aqueous
solution of a solvent, then immersing the oil-absorbing hollow membrane
prepared in step
(2) into the solvent aqueous solution for 1-20 s, and quickly taking the
membrane out and
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putting it in a coagulation bath for solidification. This yields the oil-
absorbing hollow
membrane, wherein the solvent is one of dimethylformamide, dimethylacetamide,
dimethyl sulfoxide or dimethylbenzene; and the medium of the coagulation bath
is water;
and 2) a dilute solution processing method: firstly, preparing a dilute
solution, then
immersing the oil-absorbing hollow fiber porous membrane prepared in step (2)
into the
dilute solution, carrying out pumping filtration under a negative pressure of
0.02-0.08
MPa for 3-20 s, and quickly taking the membrane out and putting it in a
coagulation bath
for solidification. This will yield the oil-absorbing hollow membrane, wherein
the dilute
solution is prepared by polymer material, additives and solvents, as each
constituent
percentage of total quantity is 0.5-6wt%, 0-12wt% and 82-99wt%, respectively.
The
polymer material is one of polyvinyl chloride, polyvinylidene fluoride,
polypropylene or
polyacrylonitrile; the additive is one of the distilled water, anhydrous
lithium chloride,
polyvinylpyrrolidone or polyethylene glycol; the solvent is one of
dimethylformamide,
dimethylacetamide, tetrahydrofuran or decahydronaphthalene; and the medium of
the
coagulation bath is the aqueous solution of the solvent, or water.
[0019] The dispersant for dispersing the graphene in the preparation method of
the
invention comprises absolute ethyl alcohol, N-methyl pyrrolidone,
tetrahydrofuran,
dimethylformamide or dimethylacetamide, etc.; and the dispersant is preferably
absolute
ethyl alcohol.
[0020] In order to guarantee efficient oil adsorption and separation, the
preparation
method of the invention is further characterized in that the specification of
the hollow
fiber porous membrane comprises pore size range of 0.1-10 [tm, and more than
50%
porosity; and the specification of the filament braided hollow tube comprises
a braiding
pitch of 400-600
[0021] The oil-absorbing hollow fiber porous membrane of the invention can be
prepared according to the preparation method of the invention. The oil-
absorbing hollow
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fiber porous membrane not only has a high oil adsorption function, but also
has a
continuous oil adsorption function, as well as an oil-water separation
function. The hollow
fiber porous membrane prepared by the preparation method of the invention can
be
applied to oil adsorption and separation, herein the hollow fiber porous
membrane is
guaranteed for non-swelling in the oils. As for the oils, toluene,
trichloromethane and
other oil low-molecular organic liquids, or kerosene, diesel and other partial
hydrocarbon
mixtures are mainly included.
[0022] The first principle that the oil-absorbing hollow fiber porous membrane
prepared by the preparation method of the invention has a continuous oil
adsorption
function is that when the surface of the oil-absorbing hollow fiber porous
membrane
prepared in step (2) is processed by using an aqueous solution of a solvent,
the hollow
fiber membrane is swelled and dissolved by the good solvent for the polymer
material of
the hollow fiber porous membrane, and further re-solidifying in a coagulation
bath, the
graphene can be embedded into the hollow fiber membrane surface, thereby
enhancing the
interface bonding strength between the graphene and the hollow fiber membrane.
[0023] The second principle that the oil-absorbing hollow membrane prepared by
the
preparation method of the invention has a continuous oil adsorption function
is that when
the surface of the oil-absorbing hollow fiber porous membrane prepared in step
(2) is
processed by using a dilute solution, the graphene can be firmly anchored to
the surface of
the oil-absorbing hollow membrane while making sure that the graphene is
exposed to the
surface of the matrix layer as a dilute polymer solution with a certain
viscosity, thereby
enhancing the interface bonding strength between the graphene and the oil-
absorbing
hollow membrane.
[0024] The oil-absorbing hollow fiber porous membrane prepared by the
preparation
method of the invention takes hydrophobic graphene as an adsorption layer and
takes an
oleophylic (non-swelling) hollow polymer fiber porous membrane as a matrix
layer. The
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membrane is prepared into a membrane assembly and put into an oil/water
solution with
one end being sealed and the other end being provided with an appropriate
negative
pressure, wherein the graphene adsorption layer has a function of oil
adsorption and
water-repellency, and the negative pressure provides power for continuous oil
adsorption-desorption. The mass transfer mechanism of continuous oil
adsorption and
separation is that the oil can be absorbed preferentially by the graphene on
the outer
surface of the oil-absorbing hollow fiber membrane, and then the oil passes
through the
hollow fiber porous membrane wall through negative pressure pumping and is
transported
to an oil storage device along the hollow pipeline, which achieves
simultaneous oil
adsorption and desorption.
[0025] Those not described in the invention are suitable for the prior art.
Hereinafter,
the invention is described in further detail by providing specific examples,
but the
protection range of the claims of the application is not limited by the
specific examples.
[0026] EXAMPLE 1
[0027] (1) Preparation of the graphene dispersion liquid: 800 ml of dispersant
dimethylacetamide and 0.24 g of graphene are added into a container, and
ultrasonic
dispersion is carried out on the obtained mixture for 30 min to obtain
homogenous
graphene dispersion.
[0028] (2) Preparation of the oil-absorbing hollow fiber porous membrane: the
polyacrylonitrile filaments braided hollow tube is prepared into an assembly
and
immersed into the graphene dispersion liquid at a temperature of 25 C,
pumping filtration
is carried out from a dead-end of hollow fiber porous membrane under a
negative pressure
of 0.08 MPa for 10 min, and then the membrane is placed in the air for
naturally drying
until excess graphene on the surface of the hollow fiber porous membrane falls
off, finally,
the membrane is put in a vacuum oven under a negative pressure of 0.1 MPa for
drying at
a room-temperature for 10 h.
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[0029] (3) Processing of the surface of the oil-absorbing hollow fiber porous
membrane:
first, a dilute solution is prepared, polyacrylonitrile which is 1% of the
total mass of the
dilute solution, polyvinylpyrrolidone which is 6% of the total mass of the
dilute solution
and dimethylacetamide which is 93% of the total mass of the dilute solution
are mixed and
stirred at 70 C for 1 h to form a uniform transparent solution, then the oil-
absorbing
hollow membrane prepared in step (2) is immersed into the dilute solution,
filtration is
carried out at a negative pressure of 0.8 bar for 7 s, and the membrane is
quickly taken out
and put into water for solidification to obtain the final product.
[0030] Performance examination: the water intake pressure of the product
hollow fiber
membrane is 0.016 MPa , and the kerosene flux measured under 0.01 MPa is 12733
L/m2. h.
[0031] EXAMPLE 2
[0032] (1) Preparation of the graphene dispersion liquid: 600 ml of dispersant
absolute
ethyl alcohol and 0.3 g of graphene are added into a container, and ultrasonic
dispersion is
carried out on the obtained mixture for 30 min to obtain homogenous graphene
dispersion.
[0033] (2) Preparation of the oil-absorbing hollow fiber porous membrane: the
polyvinyl chloride hollow fiber membrane is prepared into an assembly and
immersed into
the graphene dispersion liquid at a temperature of 20 C, pumping filtration
is carried out
from a dead-end of hollow fiber porous membrane under a negative pressure of
0.06 MPa
for 30 min, and then the membrane is placed in the air for naturally drying
until excess
graphene on the surface of the hollow fiber porous membrane falls off, finally
the
membrane is put in a vacuum oven under a negative pressure of 0.1 MPa for
drying at a
room temperature for 12 h.
[0034] (3) Processing of the surface of the oil-absorbing hollow fiber porous
membrane:
the oil-absorbing hollow membrane prepared in step (2) is immersed into 80 wt%
of
toluenedimethylbenzene aqueous solution and taken out after 3 s and then
immediately put
CA 02898815 2015-07-27
into water for solidification to obtain the final product.
[0035] Performance examination: the water intake pressure of the product
hollow fiber
membrane is 0.065 MPa, and the kerosene flux measured under 0.056 MPa is
126.32
L/m2. h.
[0036] EXAMPLE 3
[0037] (1) Preparation of the graphene dispersion liquid: 800 -ml of
dispersant absolute
ethyl alcohol and 0.32 g of graphene are added into a container, and
ultrasonic dispersion
is carried out on the obtained mixture for 35 min to obtain homogenous
graphene
dispersion.
[0038] (2) Preparation of the oil-absorbing hollow fiber porous membrane: the
polyvinylidene fluoride hollow fiber membrane is prepared into an assembly and
immersed into the graphene dispersion liquid at a temperature of 20 C,
pumping filtration
is carried out from a dead-end of hollow fiber porous membrane under a
negative pressure
of 0.08 MPa for 20 min, and then the membrane is placed in the air for
naturally drying
until excess graphene on the surface of the hollow fiber porous membrane falls
off, finally,
the membrane is put in a vacuum oven under a negative pressure of 0.1 MPa for
drying at
a room-temperature for 12 h.
[0039] (3) Processing of the surface of the oil-absorbing hollow membrane: the
oil-absorbing hollow membrane prepared in step (2) is immersed into 100 wt% of
dimethylacetamide solution and taken out after 1 s and then immediately put
into water for
solidifying to obtain the final product.
[0040] Performance examination: the water intake pressure of the product
hollow fiber
membrane is 0.06 MPa, and the kerosene flux measured under 0.044 MPa is 88.24
L/m2.h.
[0041] EXAMPLE 4
[0042] (1) Preparation of the graphene dispersion liquid: 500 ml of dispersant
absolute
ethyl alcohol and 0.20 g of graphene are added into a container, and
ultrasonic dispersion
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is carried out on the obtained mixture for 20 min to obtain homogenous
graphene
dispersion liquid.
[0043] (2) Preparation of the oil-absorbing hollow fiber porous membrane: the
polypropylene hollow fiber membrane is prepared into an assembly and immersed
into the
graphene dispersion liquid at a temperature of 20 C, pumping filtration is
carried out
from a dead-end of hollow fiber porous membrane under a negative pressure of
0.08 MPa
for 20 min, and the membrane is placed in the air for naturally drying.
[0044] (3) Processing of the surface of the oil-absorbing hollow fiber porous
membrane:
first, a dilute solution is prepared, polypropylene which is 1% of the total
mass of the
dilute solution and decahydronaphthalene which is 99% of the total mass of the
dilute
solution are mixed and stirred at 180 C for 1h to form a uniform transparent
solution.
Then, the oil-absorbing hollow fiber porous membrane prepared in step (2) is
immersed
into the dilute solution, filtration is carried out at a negative pressure of
0.08 MPa for 7 s,
and the membrane is quickly taken out and put into ethyl alcohol for
solidification to
obtain the final product.
[0045] Performance examination: the water intake pressure of the product
hollow fiber
membrane is 1.3 bar, and the kerosene flux measured under 0.084 MPa is 1398.86
L/m2.h.
[0046] The continuous oil adsorption and oil-water separation performance
tests are
carried out on the oil-absorbing hollow fiber porous membrane prepared in
examples 1-4
in the invention: the continuous oil adsorption device being used is a well-
known common
membrane filtration device (referring to Fig. 1). Firstly, the oil-absorbing
hollow fiber
porous membrane is prepared into a membrane assembly 3 and suspends at the
interface
of the kerosene 2 and water 1. A circulating water vacuum pump 7 provides an
appropriate
negative pressure for pumping oil and water. The oil is preferentially
absorbed by the
graphene on the outer surface of the oil-absorbing hollow fiber membrane and
is desorbed
through negative pressure pumping. Meanwhile, the oil passes through the
hollow fiber
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porous membrane wall and is transported to a liquid storage tank 6 along the
hollow
pipeline orderly through a pressure gauge 4 and a valve 5. The liquid storage
tank 6 is
connected with the circulating water vacuum pump 7 through a pipeline.
[0047] Before measuring the kerosene flux of the oil-absorbing hollow fiber
membrane,
the critical water intake pressure is measured, and then under a condition of
below the
critical pressure, the measurement for kerosene flux can be carried out in
guarantee that
the oil-absorbing hollow fiber porous membrane only absorbs oil but not water.
The test
results are shown in Table 1. The continuous oil adsorption device test shows
that the
oil-absorbing hollow fiber porous membrane can simultaneously carry out
continuous oil
adsorption and oil-water separation, and the continuous oil adsorption of the
oil-absorbing
hollow membrane can be realized. The kerosene flux table (table 1) of the oil-
absorbing
hollow membrane means that the oil-absorbing hollow fiber porous membrane has
a
continuous oil adsorption function.
[0048] Table 1. Kerosene Flux of the Oil-Absorbing Hollow Membrane Prepared In
the
Examples
Test Time (min)
pressu
________________________________________________________________________
Examples
re
2 4 6 8 13 18 23 28 33
(bar)
Example I
kerosene
0.1 12733 12233 12103 11973 11687 11478
10905 10123 8639
flux
(L/m2.h )
Example 2
kerosene
0.56 126.32 116.24 109.78 95.54 93.23 90.38
88.76 86.21 86.13
flux
(L/m2.h)
Example 3
kerosene
0.44 88.24 82.75 80.65 78.59 71.78 66.57
60.63 55.75 51.43
flux
(L/m2.h )
Example 4
kerosene
0.84 1398.86 1391.73 1388.39 1385.94 1382.78 1380.64
1378.67 1377.85 1377.70
flux
(L/m2.h )
13
