Note: Descriptions are shown in the official language in which they were submitted.
~ Jr~ r~
HOECHST AKTIENGESELLSCHAFT HOE 91/F 336 Dr. MI
Description
Semipermeable, poxou , asymmetric polyether amide
membranes
Since the introduction of asymmetric membranes of cel-
lulose acetate by Loeb and Sourixajan ~S. Sourixajan,
Reverse Osmosis, Logos Press, London 1970) and of hydro-
phobic polymers (~S Patent 3,615,024) a number of
membrane have been developed and proposed, in particular
for separation of low and high molecular constituent~
dissolved in water, the ~tructure and suitability of
which are given in the literature (Desali~ation, 35
(1980), 5-20) and which have also been successfully
tested in industrial practice or for clinical purposes.
Many of the membranes described have particularly advan-
tageous properties for achieving specific tasks. As a
result of their chemical constitution and their struc-
ture, each individual membrane can be optimally suited
only for quite ~pecific separation problems. From this
results the fundamental requirement of continuously
developing new membranes for new tasks.
EP-A 0 082 4~3 gives an overview of the advantages and
di~advantages of membrane~ which are already known. Thus,
for example, there are hydrophilic, asymmetric membranes
of cellulose acetate having satisfactory antiadsorptive
properties, but whose thermal and chemical stability
leave a lot to be desired. Membranes of poly~ulfones or
similar polymers do posse~s a good thermal and chemical
stability, but such membranes, because of the hydrophobic
properties of the polymer~ used, show a pronounced
tendency to adsorb dissolved Rubsta~ces, as a result of
which the membrane is blocked. The mixtures of
polysulfone and polyvinylpyrrolidone di3closed in
EP-A 0 082 433 do dispose of the disadvantage resulting
from the hydrophobicity of the polysulfone, but these
- 2 ~ t~
mixtures are sen3iti.ve to the action of organic solvent~.
Hydrophilicity and simultaneous resistance to solvents
are found in membranes of regenerated cellulose; but
these can be relatively easily hydrolyzed in acid or
alkaline media/ and moreover they are easily attacked by
microorganisms.
It is therefore an ob~ect of the invention to provide
semipermeable, porous asymmetric membranes which are
stable to chemical and thermal action, which can be
prepared by a simple and economical method and wbose
membrane properties can be easily varied according to the
area of application.
This object is achieved by a semipermeable, porous,
asymmetric membrane whose distinguishin~ features are
that it contains a polyaramide which contains one or more
of the recurring structural units of the formula (I)
O O
¦¦ ll (I)
-~-Ar-C-
and, based on the sum of (II) and (III), up to 15 to 100
molar ~ of structural units of the formula (II)
~ u ~ ~ ~~ (II)
and, based on the sum of (II) and (III), up to 0 to 85
molar % of structural units of the formula (III)
-NH~ ~NH-
( I I I )
where the ratio of the sum of (II) and (III) to (I) i5
0.90 to 1.10, but preferably 1~0
and the ~ymbols -AI-, -X- and -Y- have the following
- 3 ~ p~.,~
meaning:
-Ar- i8 a divalent, aromatic or heteroaromatic radical,
where the two ca.rbonyl gra,up~ are located on
unad~acent ring carbon atom~ (.i.e. in para- or meta-
position) and the Ar rsdical is un~ub~tituted or
substituted by one or ~wo branched or unbranched
C~-C3-alkyl or C~-C3-alkoxy radicals, aryl or aryloxy
radical~ or Cl-C6 perfluoroalkyl or C~C6-perfluoro-
alkoxy radical~ or by fluorine, chlorine, bromine or
lQ iodine;
-X- i~ a group -C~CH3)2-, ~C(CF3)2-, -CO-, -S~ , SO2 ,
-CH2-, -S- or ~O- or a direct bond
and
-Y- is a group SO2-, ~ C~, -CH2-, -O-, -S-,
-C( CH3 ) Z~ ~ -t (CH 1)2~3C(CH9)2- -
~ or -C(CF3) 2- or
a direct bond.
According to the invention therefore, for the formation
of the polyaramides contained in the membrane, one or
more dicarboxylic acid derivatives of the formula ~I) and
diamine component~ o the formula ~II) and, possibly,
(III) are necessary, the ratio of the ~um of (II) and
(III) to (I) being 0.90 to 1.10. Stoichiometric amounts
of carboxylic acid derivati~es and diamine components are
preferably u~ed.
To prepare the polysramide~ required according to the
invention, the following compounds are ~uitable:
one or more dicarboxylic acid derivatives of ~he formula
(I'~
Cl-C-A~-C-Cl
(I')
O O
for example terephthalyl dichloride and/or isophthalyl
- 4 ~
dichloride, where the aroma~ic rincl i~ unsubstituted or
is qubstituted by one or two branched or unbranched
Cl-C3-alkyl or C1-C3-alkoxy radicals, aryl or aryloxy radi-
cals or Cl~C6-perfluoroalkyl or c1-CB-perfluoroalkoxy
radicals or by fluorine, chlorine, bromine or iodine.
Aromatic diamines of the formula ~II'),
H H
~~ ~D~ ~1 (II'
for example 2,2'-bis[4-~4'~aminophenoxy)phenyl]propane,
bis~3-(3~-aminophenoxy)phenyl] sulfone, bis[4-(4'-amino-
phenoxy)phenyl] sulfone, bis[4-(4~-aminophenoxy)phenyl]-
methane, 2,2'-bis[4-(4'-aminophenoxy)phenyl]hexafluoro
propane and, possibly, aromatic diamines of the formula
(III')
~2N ~ ~ ~2 (III')
for example: bis[3-aminophenyl] sulfone, bis[4-amino-
phenyl] sulfone, 1,4-bis[4'-aminophenoxy)benzene, bist4-
aminophenyl)methane, bis[4,4'-aminophenyl) ether,
bis[3,4'-aminophenyl) ether.
The ~olution condensation of aromatic dicarboxylic acid
dichloride~ of the formulae (I') with aromatic diamines
of the formulae (II') and, po sibly, (III') is carried
out in aprotic polar solvents of the amide type, ~uch as
for example in N,N-dimethylacetamide or in particular in
N-methyl-2-pyrrolidone (NMP). If required, halide salts
of the first and second subgroup of the Periodic Table of
Elements can be added to these ~olvents in a known manner
to increase the dissolving power or to stabilize the
polyamide solution~. Preferred additives are calcium
chloride and/or lithium chloride.
- 5 ~
The polycondensation temperatures are conventionally
between -20C and ~120C, preerably between +10C and
+100C. Particularly good results are achieved at reac-
tion temperatu~es between +10C ancl +80C. The polycon-
densation reactions axe preferably carried out BO that
after the reaction is completed, 3 to 50 % by weight,
preferably 5 to 35 % by weight, of polycondensate is in
the solution.
The polycondensation can be terminated in a conventional
manner, for example by addition of monofunctional
compounds, such as b~nzoyl chloride. After completion of
the polycondensation, i.e. when the polymer 301ution has
attained the Staudinger index required for further
processing, the hydrogen chloride formed bound to the
amide solvent is neutralized by addition of basic sub-
stances. Suitable substances for this are for example
lithium hydroxide, calcium hydroxide, in particular
calcium oxide. After neutralization, the solutions are
filtered and degassed and mem~ranes are drawn from these
solutions. The concentration of the solutions and also
the molecular weight of the polymers represent the most
important production parameters, since by this means the
mem~rane properties ~uch as porosity, mechanical
stability, permeability and retention capacity may be
adjusted.
The Staudinger index is a mea~ure for the mean chain
length of the resulting polymers. The Staudinger index of
the polyaramide is in the range from 50 to 1000 cm3/g~
preferably in the range from 100 to 500 cm3/g, particu-
larly preferably in the range from 150 to 350 cm3/g. It
was determined in solutions having 0.5 g of the
particular polymer in 100 ml of 96% strength sulfuric
acid at 25C.
The Staudinger index [~] (limiting viscosity, intrinsic
viscosity) i8 taken to mean the expression
- 6 ~ 3
lim P = [ ~7 ]
C2 -- C2
where
C2 = concentration of the di3solved substance
~5p - sp~cif~c viscosity
= -- --1
~1
~ = viscosity of the solution
~1 = viscosity of the pure solvent.
To produce the membrane according to the invention from
polyaramides, the polyamide solution already described is
filtered, degassed, and then, in a known manner using the
phase inversion process (Robert E. Kesting, "Synthetic
Polymeric Memhranes", 2nd Ed., 1985, p. 237 ff . ), an
asymmetric porous membrane i~ produced. For thi~ purpose
the polymer solution is spread as a liquid layer on a
~pport as flat a~ possible. The flat support can for
example comprise a glass plate or a metal drum. A
precipitant liquid is then allowed to act on the liquid
layer, which liquid is miscible with the solvent of the
solution, but in which the polymers dissolved in the
polymer solution are precipitated as a membrane.
Further suitable colvent constituent~ are readily
volatile substance3 such as for example tetrahydrofuran,
acetone or methylene chloride. Suitable prec~pitant
liquids are water, mono- or polyhydricalcohols such as
methanol~ ethanol, isopropanol, ethylene glycol or
glycerol, or, additionally, mixtures of the~e sub~tanceQ
with each other or with aprotic, polar ~olvent~ such as
N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl
sulfoxide, but in particular with N-methyl-2-pyrrolidone.
As a result of the action of the precipitant liquid on
the liquid layer the polyaramides dissolved in the
polymer solution are precipitated from thi~ solution with
the formation of a porou~ film having an asymmetric pore
- 7 ~. fn,~
structure.
The ~eparation efficiency and the rejection efficiency of
the membranes according to the invention can be specifi-
cally varied by addition of polyvinyl pyrrolidone (PVP)
S to the solution of the polyaramide prior to the coagula-
tion or by carrying out the polycondensation of the
structural units (I), (II), and, possibly, (III) in the
pre~ence of PVP or by a Rubsequent treatment at a
temperature in the range of 60-140C, preferably in the
range of 60-100C, with a liquid, for example with water,
mixtures of water with mono- or polyhydricalcohol~ or
also for example polyethylene glycol, or with polar,
aprotic solvents of the amide type, ~uch as N-methyl-
pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide or
mixtures of these liquids with each other or alter-
natively by treatment with ~team, which may be
superheated.
A thermal post-treatment of the membranes according to
the invention leads to a compres ion of the active layer,
20 80 that a subsequent adju~tment of the rejection
efficiency i5 possible in this manner.
As a result of the addition of polyvinylpyrrolidone to
the polymer solution it is possible to achieve an
increase in hydrophilicity and separation efficiency of
the membranes according to the invention by preparation
of a homogeneously miscible polymer blend and to achieve
a better processability. The increa~ed hydrophilicity of
the integrally asymmetric membrane leads to a reduced
blockluging tendency, i.e. tc an expedient fouling
behavior (lower decrea~e in ilux per unit of time and
stabilization of the product flux at a hiyh level).
When there is an addition of polyvinylpyrrolidone, this
is added in amounts of 1 to 80 ~ by weight, preferably 5
to 70 % by weight, particularly preferably 20 to 60 % by
weight, relative to the ma~ of the polyamide.
~he molecular weight of the polyvinylpyrrolidone in thi~
~ ~ r, " "~ 3
f~
case is in the range from 10,000 to 2,000,000 dalton
(g/mol) (given as weight average~, preferably in the
range from 20,300 to 1,000,000, particularly preferably
in the range from 30,000 to 95,000 dalton.
When the process i~ carried Ollt, the precipitant liquid
is advantageously allowed to act on the membrane
precipitated by this, until virtually all of the solvent
in the membrane has been replaced by precipitant liquid.
The membrane formed is then freed from precipitant
liquid, for example by drying the membrane directly in an
air stream having a relativ~ humidity in thP range from
20 to 100 % or by fir~t treating it with a softener such
as glycerol, or glycerol/water mixtures and then drying
it.
To produce membranes which are arranged on a support
layer, which is permeable to flowable media, the
procedure as deRcribed above i~ carried out but the
support used for forming the membrane layer iR a fabric
or a nonwoven web, for example of plastic, for example
polypropylene, polyethylene andtor polyethylene tere-
phthalate, or of paper and after the membrane layer has
been formed this is left on the support. However, the
membrane can alternatively be first prepared without a
support and only then applied to a permeable support.
Flat membranes produced in this manner have a thickness
without support in the range from lO to 300 ~m, in
particular in the range from 20 to 150 ~m. In a known
manner (Mark C. Porter, "Handbook of Industrial Membrane
Technology", 1990, p. 149ff), hollow fibers and capil-
laries can alternatively be produced from the solution ofthe polyaramides, by spinning the polymer solution in
accvrdance with the prior art through an appropriately
designed shaping ring nozzle or hollow needle nozzle into
a precipitant liquid. The wall thickness of such capil-
laries or hollow fibers is conventionally in the rangefrom 20 to 500 ~m, in particular 80-200 ~m.
If the membrane is qoaked in glycerol after the
coagulation, it can contain glycerol for example in the
range from 5 to 60~, relative to its total weight;
membranes impregnated in this manner are dried, for
example at a temperaOture of 50C.
The membrane according to the invention, apart from
standard ~pplications of porou~ me~ranes known to those
skilled in the art, such as pressure filtration (micro-l
nano- and ultrafiltration), diafiltration and dialysis
are likewise auitable as support m~mbranes for selec-
tively permeable layers (for example for gas separation,
pervaporation) which are produced directly on or in the
membrane. Thus for example "ultrathin" layers (s 1 ~m)
compo~ed of polymers having functional groups (for
example silicones, cellulose ethers, fluorine copolymers)
can be spread on water~ applied to the membrane surface
from there and for example can be covalently fixed by
reaction with a diisocyanate, in order to achieve more
selective permeability by this means. Further methods for
transfer of thin Yelectively permeable layers are known
to those skilled in the art. By analogy, the membranes
according to the invention are also suitable as supports
for reactive molecules, for example to fix enzymes or
anticoagulants such as heparin according to the prior
art.
The thickness of the membranes according to the invention
without support layer is in the range from 10 to 300 ~m,
in particular from 20 to 120 ~m.
Examples:
Membranes of homo- and copolyaramide~
For the membranes studied in the examples, the corre-
sponding polyaramides were prepared as described above in
N-methylpyrrolidone (NMP) as solvent by a polycon-
denqation at 50C.
A solution of this polyaramide was applied to a nonwoven
support web of polypropylene and was coagulated in water
at 20~C.
The permeate flux of an ultrafiltration membrane produced
-- 10 ~ " r ~ ; f~
in this manner ~nd the rejection eff:iciency for dissolved
macromolecules were determined at pressures of 3.0 bar at
20C in a stirred cylindrical cel.l (500 rpm/ 250 ml,
membrane surface area 38 cm2)~
5 The rejection efficiency is by defi:nition
C~- C2
R = ~ 100 ~
Cl is the concentration sf the aqueous test solution,
C2 is the concentration in the permeate.
Example 1: ~ 9S molar ~ of terephthalyl dichloride
(TPC)
100 molar % of 2,2'-bis[4-(4' amino-
phenoxy)phenyl]propane (BAP)
15 Example 2: ~ 95 molar ~ of TPC
100 molar % of bi [4-(4'-aminophenoxy)-
phenyl] sulfone (BAPS)
Example 3: 2 95 molar % of isophthalyl dichloride
(IPC~
100 molar % of BAP
Example 4: 2 95 molar % of (O.8 TPC + O.2 IPC)
100 molar ~ of BAP
Example 5: > 95 molar ~ of TPC
70 molar % of BAP + 30 molar ~ of bis(4-
aminophenyl) sulfone
Test substances for the rejection determination and
additives used:
The test solutions used were aqueou~ polyvinylpyrrolidone
solutions and aqueous solutions of fractionated dextrans.
The density measurementR were carried out using a density
measuring apparatus ~DA 210 from the Kyoto ~lectronics
company.
K 30. polyvinylpyrrolidone (M~ 43,000) (~LIviskol
2 % strength aqueous solution K30, ~A5lF),
T 10: dextran ~MW lO,000) (~Dextran T10,
1 % strength aqueGus ~olution Ph2~nhcia),
Dextran (qDextran blue,
blue: dextran with dye labeling Pharnacia),
(MW 2,000,000)
0.5 ~ strength aquecus solution
K 90: poly~inylpyrrolidone (~W 1,200,000~ uviskol KgO, E~SF)
Aerosil.pyrogenic silica gel (Aerosil 200,
Degus~a)
- 1 2
-
H ~! _
,~ o n
~ E~
c~ l~c~
~ ~ ~ 0 ~n
.~ ~ XI ~ ~ ~ r~
. . _. O-- -- ~ ~1
H ;op ~ -- E ~ _ .~
~ ~ _ ~ ~ o o ~ a)
~ - æ ~ I o~ ~ ~
o ~ ~c ~7
~ ~ 8 ~ ~ ~I ~ n ~ ~ ~ ` ,~
~ ~ ~ a o oo ~co ~ ~
~ _ ~ ~ ~
t ~ '.~ _ .
~ ~dP ~1~ ~- +
~ ~ -- N ~ .
- 13 ~
u~ing homopolyaramide3 of TPC and }3~P, membranes can be
produced in a very hroad concentration range. If the
viscosity i~ adjusted ~o [~] - 110 ml/g, all membranes
having a polyme.r concentration greater than 20 ~ are not
permeable to water and aqueous solutions up to 40 bar. As
the polymer concentration falls, ~he permeability to
water very sharply increa~es. The rejection values of the
test substances K30 and T10 behave inversely. While the
rejection of ~30 only decrea3es gradually because of the
broad molecular weight di~tribution of the polyvinyl-
pyrrolidone, the rejection of dextran T10 (narrow
molecular weight di~trlbution) decreases very rapidly to
values which can no longer be measured.
- - - - - ~
E ~ CO N tO l U~
, ~tl __
r--
~ ~ CO ~D ~ l O~
:~~ _ _
~P U~ C~ Lt~
~ ~ o~ ~ l l
.~ O O O
~ _I ~1 N N ~) l C~ .~
~O _ _ , _ ;~
~q ~o oO n COD O
.~ ~-- .
~ ~.~."
Q) ~ ~ O O O O
~2 p~ o _l u) o ~
~ ~ ~ _ _ -'t
N 1~ ~ ~ _ --I 2 1~
- 15 - ~3t,.,~
From the preceding table it can be seen that PVP-
containing membranes, compared to PVP-free membrane~,
have an increaLsed ~ater flux, ~ith approximately equal
reject.ion effi.ciencies (see C2 = 17.5 ~ and PVP addition
S O and 50 %). In addition it can be seen that a membrane
produced from a 20 % strength polymer solution which i~
not permeable to water is made permleable by PVP addition.
-- 16 --
, ` ?~
' _ - I _ _ _ ,
1~ 1~ ~o
~ In I~ ~ U~ C~ O
_ ~ er I_ r- r~ ~o
.~
.~ o
rl n~ d~ ~ r~ e~' O ~ ~0
æ~ ~ QO ~ CD ~ ~ O~
_ _
Ul $ O O O
_ ~ U~ _, _, ~ ~ _,
~.~ ~_. ~
~ _, O~ ~, 0 U~ ~
~'' . _ ' .
;~ ~ O l o ~ o ~ ~
H ~ . . g
.~ _~ ~
~ a o o .~ D
`; '3
- 17 -
A polyaramide membran~ (from a 17 5% strength solution
without PVP) i5 heated for 10 minute~ at 100C in water.
As a result of this treatment, analogous to a sintering
process, the membrane covering layer compresses and the
rejection value increases. While the K30 rejection is
already quantitative from a heating temperature of 80C
(not given in the table), the T 10 rejection increases
from approximately 80% ~o 97%. A thermal treatment of
this aramide membrane allows an individual membrane to
be adjusted so that it can find an application in the
ultrafiltration region and in the neighboring nano-
filtration region.
If a thermal post-treatment is given to PVP-containing
membranes, analogously to the case without PVP addition,
a compression of th~ membrane covering layer results with
increase of the rejection ~alues for the test substances.
Analogously to Table 1.2, higher permeabilities are also
shown here with PVP-containing membranes in comparison to
their PVP-free variants.
A 50% PVP addition and heating for 10 minutes at 100C
gives a membrane having 96~ rejection for T10 and a water
~flux of 80 l~m2h. The comparable membrane without PVP, at
an approximately equal rejection of 97~, ha~ a water flux
of only 55 l/m2h.
,.
- 18 - 2 ``J ';"' ' -
1.4) Polyaramide hollow fiber membrane
Internal diameter - 102 mm
Stream flow rate 3-4 m/s, t:ransmem~rane pressure
3.5 bar
C2 = lS~ in NMP
Th~E1 M~*~ane Water Rejection Permeate
treatment layer flux [~] flux
[mln/~C] t[h~m]kne5S [l/~h] K 30 [l/~h]
_ ____ _
_ 250 40 76 20
e _
10/100 220 30 80 15
A polyaramide hollow fiber is individually stretched
between two needles and is tested with the aid of a pump
and an externally applied pressure using the crossflow
technique. The pxessure is measured at the inlet and
20 outlet of the hollow fiber and the transmembrane pressure
(TMP) is determined therefrom [TMP = ~PE + PA/)2]
PE = inlet pressure PA = outlet pressure
-- 1 9 '~ J ~ 3
_ o_ _ _ .
~o ~ t~ o
o
t o
~ ~ -- U~ ~7 ~ O
__ ~ ~
~ _. t t~, t~ .~ ~
~ ~ ................................. ~ ~
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,~UO~ .~ ~ ~ ~ ~ ~ ~ ~.~
~ 11 ~ dP dl dP ~ dP dP ~ ~
l ~ ~ ~ ~1 _i ~ Ln, U~ ~ ~ ~
t ~ ~ ~ .,~
~ _5 ~ _, _, "~
-- 20 --
.r3
-_ ~ ~ r
~t_ _
.
.~o o~ ~ o~
,. . ~ _ _ _ . ~ ~
~o o o ,o o o o ~ g
_ _ __ ~a
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@ ~ ~ ~ ~ ~o ~o o~ ~o ~ ~o o ~o ~ ~
_
~ .- .~ .
~ .~ O O 0~ O i~ ~æ
~ ~ ~ l c~; P~ l P~ x ;n n K
b _ ~ ~ ~
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21 -
e .~ ~ ~
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-- 22 --
~ If~ .
9 ~ , 9
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