Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
-1-
A PROCESS FOR SEPARATING HYDROGEN FROM GAS MIXTURES
USING A SEMI-PERMEABLE MEMBRANE CONSISTING PREDOMINANTLY
OF POLYCARBONATES DERIDED FROM TETRAHALOBISPHENOLS
This invention relates to a process for
separating hydrogen from gas mixtures using a semi.-
permeable membrane derived from polycarbonate
polymers.
In various industries, it is necessary or
highly desirable to separate one component from
another in a gaseous stream. Processes used to
perform such separations include cryogenics, pressure
swing adsorption, chemical absorption, and membrane
separations.
Membranes have been used to recover or isolate
a variety of gases, including hydrogen, helium,
oxygen, nitrogen, carbon monoxide, carbon dioxide,
water vapor, hydrogen sulfide, ammonia; and light
hydrocarbons. Applications of particular interest
include the separation of hydrogen Erom gas mixtures
such as mixtures containing nitrogen, carbon monoxide,
carbon dioxide, and/or light hydrocarbons. For
example, the separation and use of hydrogen is often
37,692-F -1-
_2_ ;. ; ; , ;_i ,.:; , :u.
W, ;,~_ .' !. v
necessary in various hydrocracker, hydrotreater, and
catalytic cracking processes used in the oil refinery
industry. Membranes can be used to achieve such
separations.
Such membrane separations are based on the
relative permeability of two or more gaseous
components through the membrane. To separate a gas
mixture into two portions, one richer and one leaner
in at least one component, the mixture is brought into
contact with one side of a semi-permeable membrane
through which at least one of the gaseous components
selectively permeates. A gaseous component which
selectively permeates through the membrane passes
through the membrane more rapidly than at least one
other component of the mixture. The gas mixture is
thereby separated into a stream which is enriched in
the selectively permeating component or components and
20__ a.stream which is depleted in the selectively .
permeating component or components. The stream which
is depleted in the selectively permeating component or
components is enriched in the relatively non-
permeating component or components. A relatively non-
ermeatin com onent
P g p permeates more slowly through the
membrane than at least one other component of the
mixture. An appropriate membrane material is chosen
For the mixture so that some degree of separation of
the gas mixture can be achieved.
Membranes for hydrogen separation have been
fabricated from a wide variety of polymeric materials,
including cellulose esters, polyim.ides, polyaramides,
and polysulfones. An ideal has separation membrane is
characterized by the ability to operate under high
37,692-F _2_
. ' ;-' ~~ J.
'' a ' - '.
~~ 5 n
_3_
temperature and/or pressure while possessing a high
separation factor (selectivity) and high gas
permeability.
A problem of the prior art is finding membrane
materials which possess all the desired
characteristics. Polymers possessing high separation
factors generally have low gas permeabilities, while
those polymers possessing high gas permeabilities
generally have low separation factors. In the past, a
choice between a high separation Factor and a high gas
permeability has been unavoidably necessary.
Furthermore, some of the membrane materials previously
used suffer from the disadvantage of poor performance
under hi h o eratin tem eratures and
g F g p pressures.
A membrane capable of separating hydrogen from
light hydrocarbons which possesses high selectivity,
high gas permeability, and ability to operate under
extreme conditions of temperature and pressure i-s
needed.
The invention is a process of separating
hydrogen from gas mixtures comprising:
(A) contacting one side oz a semi-permeable membrane
with a feed gas mixture containing hydrogen under
pressure, wherein the membrane divides a separation
chamber into a higher pressure side into which the
feed gas mixture is fed and a lower pressure side;
(B) maintaining a pressure differential across the
membrane under conditions such that hydrogen
selectively permeates through the membrane from the
37,692-F -3-
_t~_
high pressure side to the low pressure side of the
membrane;
(C) removing from the low pressure side of the
membrane permeated gas which is enriched in hydrogen;
and
(D) removing from the high pressure side of the
membrane non-permeated gas which is depleted in
hydrogen;
wherein the membrane comprises a thin discriminating
layer comprising a polycarbonate polymer derived from
a bisphenol corresponding to Formula I:
Formula I
R R
_. ._.__ H0 ~ R1 ~ 0H __
,
R ~° R
wherein R at each occurrence is independently
hydrogen, chlorine, bromine, or C1_~ alkyl, and
R1 is -CO-, -S-, -S02-, -0-, a C1_6 divalent
hydrocarbon radical, a C1-6 divalent fluorocarbon
radical, or an inertly substituted G1-6 divalent
hydrocarbon radical, with the proviso that at least
about 25 weight percent of the moieties derived from
the bisphenol of Formula I present in the
discriminating layer bear R groups which are
exclusively bromine or chlorine and
37,692-F .-4-
- _. , -' ~~
-5- ,<~,. .
(A) contacting one side of a semi-permeable membrane
with a feed gas mixture containing hydrogen under
pressure, wherein the membrane divides a separation
chamber into a higher pressure side into which the
feed gas mixture is fed and a lower pressure side;
(B) maintaining a pressure differential across the
membrane under conditions such that hydrogen
selectively permeates through the membrane from the
hi h ressure side to the low
g p pressure side of the
membrane;
(C) removing from the low pressure side of the
membrane permeated gas which is enriched in hydrogen;
and
(D) removing from the high pressure side of the
membrane non-permeated gas which is depleted in
hydrogen,
wherein the membrane comprises a thin discriminating
layer consisting predominantly of a polycarbonate
polymer derived from a bisphenol corresponding to
R R
H0 ~ R1 ~ OH
R ~ R
wherein R at each occurrence is independently
hydrogen, chlorine, bromine, or C1_4 alkyl and R1 is
-CO-, -S-, -S02-, -0-, or a C1-6 divalent hydrocarbon
37,692-F _5-
_6_ ;.::
radical, a C1_6 divalent fluorocarbon radical, or an
inertly substituted C1_6 hydrocarbon radical, with the
proviso that at least 25 weight percent of the
moieties derived from said bisphenol present in the
discriminating layer bear R groups which are
exclusively bromine or chlorine and wherein said
membrane processes a separation factor between
hydrogen and light hydrocarbons of at least 25 at a
temperature of 25'C.
In a preferred embodiment, the thin
discriminating layer consists predominantly of a
polycarbonate polymer derived from between 50 and 100
weight percent of a bisphenol of
x x
_. .. _ HO . ~ R 1 ~ OH
X~ ~X
30
37,692-F -6-
.~7_
5 R2 R2
HO ~ R1 ~ OH
R 2 r-~.. R 2
and between 0 and 50 weight percent of a bisphenol of
wherein
R1 is a C1_6 divalent hydrocarbon radical;
R2 is C1_~ alkyl; and
X is chlorine or bromine.
The membranes used in this invention
demonstrate surprisingly high separation factors and
high permeabilities for the separation of hydrogen
from gas mixtures. In a preferred embodiment wherein
at least 35 weight percent of the moieties derived
from Formula I present in the discriminating layer
bear R groups which are exclusively bromine, wherein
the separation factor for hydrogen and light
hydrocarbons at 25°C is at least 100. Furthermore,
the membranes used in this invention possess good
mechanical properties and therefore are useful under
more extreme conditions, for example, temperature and
pressure.
The membranes used in this invention are
prepared from polycarbonates derived from bisphenols
37,692-F _7-
;..; ,;
wherein a significant portion of the bisphenols used
to prepare the polycarbonates are tetrahalo-
substituted. More preferably, the tetrahalo-
substituents are found in the 3,5-positions on the
aromatic or phenolie rings. The presence of a
significant portion of the residue of
tetrahalobisphenols enhances the separation properties
of membranes that are prepared therefrom.
preferabl
y, at least 35 weight percent of the
moieties derived from the bisphenol of Formula I
present in the discriminating layer bear R groups
which are exclusively bromine, chlorine, or mixtures
thereof. More preferably, at least 50 weight percent
of the moieties derived from the bisphenol of
Formula I present in the discriminating layer bear R
groups which are exclusively bromine, chlorine, or
mixtures thereof. Even more preferably, at least 75
-weight percent of the moieties derived from the __ .
bisphenol of Formula I present in the discriminatin g
layer bear R groups which are exclusively bromine,
chlorine, or mixtures thereof. Even more preferably,
the polycarbonate is derived from bisphenols of
Formula I, wherein R is exclusively bromine, chlorine,
or mixtures thereof. In the embodiment wherein the
polycarbonate is prepared from tetraehlorobisphenols,
it is preferable that the polycarbonate backbone
contains 90 percent by weight or greater units derived
from tetraehlorobisphenols, more preferably 95 percent
by weight, and most preferably 100 percent by weight.
Bromine is the preferred halogen herein. Examples of
preferred bisphenols of Formula I which bear R groups
which are exclusively bromine or chlorine are 2,2
bis-(3,5-bromo-4-hydroxyphenyl)propane and 2,2
37,692-F _g_
-9- ~ ~.', ?: ,
bis(3,5-ehloro-4-hydryoxyphenyl)propane, with 2,2-
bis(3,5-bromo-~d-hydroxyphenyl)propane being most
preferred.
The polycarbonates used in this invention
preferably correspond to Formula II:
R R 0 Formula II
0 ~ R1
R R
n
20
30
37,692-F _9_
-10-
wherein R and R1 are as hereinbefore defined and n is
an integer of 50 or greater. Preferably, the
polycarbonates of this invention are derived from
between 25 and 100 weight percent of a bisphenol
corresponding to Formula III:
X X
Formula III
HO ~ R1 ~ OH
X r° '°°°~ X
and between 0 and 75 weight percent of a bisphenol
corresponding to Formula IU:
R2 R2
Formula IV
_. __. _ HC ~ R 1 ~ OH _
R2 R2
wherein R1 is as hereinbefore defined, R2 is hydrogen
or C1_~ alkyl, and X is independently in each
occurrence chlorine or bromine. Preferably, the
polycarbonate is derived from between 35 and 100
weight percent of a bisphenol of Formula III and
between 0 and 65 weight percent of a bisphenol of
Formula IVY even more preferably between 0 and 50
weight percent of a bisphenol of Formula IU, and 50
and 100 weight percent of a bisphenol of Formula III.
Even more preferably, the polycarbonate is derived
from between 75 and 100 weight percent of a bisphenol
37,692-F -1p-
-
corresponding to Formula III and between 0 and 25
weight percent of a bisphenol corresponding to
Formula IV.
In a most preferred embodiment, the poly-
carbonate is derived exclusively from bisphenols
corresponding to Forrnula III. Examples of bisphenols
within the scope of rFOrmula IU include 2,2-bis(4-
hydroxyphenyl)propane and 2,2-bis(3,5-methyl-4--
hydroxyphenyl)propane.
The polymers prepared from bisphenols of
Formula III and Formula IV preferably have recurring
~5 units which correspond to Formula U:
Formula U
X X R2 R2
--. 0
0 R1 0 _ ~I 0 1 -~~
R ~ 0 C
X X R2 R2
p q ~m
wherein R1, R2, and X are as hereinbefore defined, p
is a number between 15 and 100, q is a number between
30 0 and 85, and m is a positive real number, such that
the polymer the formula represents possesses
sufficient molecular weight to prepare a membrane with
suitable characteristics.
35 In the embodiment wherein the polycarbonate of
this invention is derived from bisphenols which
37,692-F -11-
_ - 1. :. , ' %
-i2-
correspond both to Formula III and to Formula IV, R2
is preferably C1-~ alkyl, most preferably methyl. In
a more preferred embodiment, the polycarbonate used to
prepare membranes in this invention is a copolymer of
2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane and 2,2'-
bis-(3,5-dimethyl-4-hydroxyphenyl)propane.
In the hereinbefore presented formulas, R is
preferably chlorine, bromine or C1-~ alkyl, more
preferably chlorine, bromine or methyl, even more
preferably chlorine and bromine, and most preferably
bromine. Ri is preferably a C1_6 divalent hydrocarbon
radical, more preferably a C1_6 alkylidene radical,
even more preferably a propylidene radical. The
polycarbonates of this invention can be prepared by
any process known in the art which prepares
polycarbonates with suitable properties for membrane
formation. See Encyclopedia of Polymer Science
_.& Technology, Editor Mark et al., Interscience _ _
Division of John Wiley & Sons, N.Y., N.Y., 1969,
Vol. 10, pp. 714-725. The polymers of this invention
should be polymerized to the extent that the polymers
will form a membrane with sufficient mechanical
strength to withstand use conditions. Preferably, the
polymer possesses an inherent viscosity of 0.35 or
greater and more preferably of 0.40 or greater. The
polymer preferably possesses a molecular weight of
60,000 or greater.
The membranes useful in this invention can
take any form known to one skilled in the art. In
particular, the membrane rnay be a homogeneous
membrane, a composite membrane, or an asymmetric
membrane. Furthermore, the membranes may be in the
37,692-F -12-
-13- t; ~.
form of a flat sheet, a hollow tube, or a hollow
fiber. One skilled in the art would readily know how
to prepare a membrane in any of the aforementioned
forms. As used herein, the term semi-permeable
membrane refers to a membrane which displays different
permeabilities for different species of molecules, and
therefore may be used in the separation of species of
molecules possessing different permeabilities across
the membrane. Permeate as used herein refers to those
s ecies which
p permeate through the membrane at a
faster rate than other species. Non-permeate refers
herein to those species which permeate at a slower
rate than the other species present.
Preferably, the membranes useful in this
invention are asymmetric or composite membranes, most
preferably asymmetric membranes.
20.-__ Homogeneous and composite membranes are
prepared by forming a thin discriminating layer which
is dense and free of voids and pores. Such membranes
or layers have generally the same structure and
composition throughout the membrane. In one preferred
embodiment, the
polycarbonates useful in this
invention are dissolved in a solvent, for example,
methylene chloride, chloroform, dimethylformamide,
N-methylpyrrolidinone, or dimethylacetamide.
Preferably, the solution contains polymer in weight
percents between 5 and 75, more preferably between 10
and 40, and most preferably between 15 and 20. This
solution should possess sufficient viscosity to allow
casting of the solution onto a uniform surface and
should be homogeneous. The polymer is cast on a
surface, and in the case of a homogeneous membrane, on
37,692-F -13-
.-1 u- ~ ~': r '' ~J
a surface from which the finished membrane may readily
be separated. A convenient way of carrying out this
operation is either by casting the membrane solution
onto a support surface which may be dissolved away
from the finished membrane following the drying and
curing steps, or by casting the membrane onto a
support having low surface energy, such as silicone,
coated glass, a surface to which the membrane will not
adhere, such as mercury, or a liquid with which the
polymer is substantially immiscible, such as water.
Casting is performed by pouring the solution onto the
appropriate surface and using an appropriate tool to
form a solution of the appropriate thickness. A
continuous casting process may be achieved by casting
the solution onto endless belts or rotating drums,
Thereafter, the east solution is exposed to drying or
curing conditions. Such conditions are used to remove
the solvent thereby leaving a thin discriminating
20__ layer of polymer which is homogeneous. The solution
may be dried either by exposure to a vacuum, exposure
to elevated temperatures, by allowing the solvent to
evaporate over time, or any combination thereof.
Generally, it is preferable to expose the cast
solution to elevated temperatures, preferably less
than 300°C, more preferably less than 200°C. In one
preferred embodiment, such exposure is done in a
vacuum oven or under vacuum conditions at elevated
temperatures. Preferably, the homogeneous membrane
has a thickness of between 0.5 (12.7 micrometers) and
10.0 mils (254 miercmeters), and most preferably
between 0.5 (12.7 micrometers) and 3 mils
(76.2 micrometers).
37,692-F -1u-
' fi
-15-
To prepare a composite membrane, a
homogeneous, thin discriminating layer can be formed
and thereafter adhered to a porous support after
formation. Alternatively, the porous support can be
the surface upon which the membrane is cast. In such
embodiment, the composite membrane is prepared by
casting a forming solution as a uniform coating on the
porous support which forms the support layer for the
finished membrane. Penetration of the polymer from
which the thin discriminating layer is formed into
pores of the porous supporting layer is acceptable so
long as the desired thickness of the semi-permeable
membrane is not exceeded. In a composite membrane,
the membrane is supported on a porous substrate or
structure. This porous supporting layer is
characterized in that it does not greatly impede the
transport across this layer of all components of a
fluid in contact with the porous layer. The porous
supporting layer can comprise a discriminating layer
which impedes the transportation of some fluid
components to the discriminating layer, but generally
this type of discriminating layer is not necessary or
desirable. In one embodiment, the supporting layer
can be a metal or polymeric plate with a plurality of
holes drilled through it. However, such a drill plate
is not advantageous because it can significantly
reduce the effective area of the membrane. In a .
preferred embodiment, the porous supporting layer is a
porous polymer membrane. Illustrative of such
polymeric supporting layers are cellulose ester and'
mieroporous polysulfone membranes. Such membranes are
commercially available. Where such supporting
membranes are thin or highly deformable, a frame or'
screen may also be necessary to adequately support the
37,692-F -15-
G,r ':,, ~ 1?
-16-
semi-permeable membrane. In one especially preferred
embodiment, the polymeric supporting layer is a hollow
fiber of a microporous polymer such as polysulfone,
cellulose acetate, or some other cellulose ester. The
hollow fiber itself provides adequate support for the
semi-permeable membrane layer coated on the inside or
outside surface of the fiber. Polysulfone hollow
fibers are most preferred for this application. After
the solution useful in forming the thin discriminating
la er is cast on the
y porous support, the porous
support and solution cast thereon are then exposed to
conditions for removal of the solvent so as to form
the dense skin. Such conditions are similar to those
described hereinbefore for the formation of the
homogeneous membrane.
To form an asymmetric membrane, a solution is
east as described hereinbefore, and thereafter the
-east solution is partially cured to remove a portion __
of the solvent. Thereafter, one or both surfaces of
the partially dried membrane is contacted with a water
quench so as to form a thin, non-porous,
discriminating layer on one or both sides of the
membrane under conditions such that the solvent away .
from the dense layer communicates to the dense layer
forming pores in the remainder of the membrane,
thereby forming an asymmetric membrane. Such porous
layer is present to provide support for the thin
discriminating layer without impeding the transport of
the fluid containing the components to be separated by
the semi-permeable, thin discriminating layer. The
partial curing step is performed in a manner similar
to the curing step described with respect to the
formation of homogeneous membranes.
37,692-F -16-
__ " : ~ ; . ~~ : ;
-17 ~. ;; : . . ;
Flat sheet, tubular, and hollow fiber
membranes can be formed by extrusion from an
appropriate solution of the polycarbonate in a
solvent. Such spinning is well known to those skilled
in the art, and the formation of hollow fibers which
are homogeneous, asymmetric, or composite membranes
requires the adaptation of the hereinbefore described
procedures to the hollow fiber form of the membrane.
Such adaptations are well within the skill of the art.
A referred extrusion
p process for such membranes is
disclosed in U.S. Patent X4,772,392.
Preferably, the thin discriminating layer in a
composite or asymmetric form of a membrane has a
thickness of between 0.02 and 10 micrometers, more
preferably between 0.02 and 2 micrometers.
Preferably, the supporting layer in a composite or
asymmetric form of a membrane possesses a thickness of
between 5 and 500 micrometers, more preferably between
10 and 200 micrometers.
In one preferred embodiment, the membranes are
annealed before use. It is believed that annealing
increases the separation factor. The membrane is
exposed to elevated temperatures below the glass
transition temperature for a period of time to
partially densify the polymer. This procedure may
optionally be performed under vacuum. For
tetrabromobisphenol A, temperatures between 30 and
250°C are preferred, more preferably between 50 and
z3o°c.
37,692-F -17-
a g_ ~;' -: ~.~
The membranes are fabricated into flat sheet,
spiral, tubular, or hollow fiber devices by methods
known in the art. The membranes are sealingly mounted
in a pressure vessel in such a manner that the
membrane separates the vessel into two fluid regions
wherein fluid flow between the two regions is
accomplished by fluid permeating through the membrane.
Under certain conditions, it may be highly desirable
to pravide support to the membrane when the membrane
is em to ed in a se aration a
P Y P pparatus or process., In
one embodiment, the peripheral area of the membrane is
affixed to a framing structure which supports the
outer edge of the membrane. The membrane can be
~5 affixed to the framing structure by a clamping
mechanism, adhesive, chemical bonding, or other
techniques known in the prior art. The membrane
affixed to the frame can then be sealingly engaged in
the conventional manner in a vessel so that the
20_ membrane surface inside the framing support separates
two otherwise non-communicating compartments in the
vessel. The skilled artisan will recognize that the
structure which supports the membrane can be an
integral part of the vessel or even the outer edge of
25 the membrane. The membrane divides a separation
chamber into two regions, a higher pressure side into
which the feed mixture is introduced and a lower
pressure side. One side of the membrane is contacted
30 with the feed gas mixture under pressure, while a
pressure differential is maintained across the
membrane. The hydrogen in the gas mixture selectively
passes through the membrane more rapidly than the
other components in the gas mixture. Gas which is
35 enriched in hydrogen is thus obtained on the low
pressure side of the membrane as permeate. Gas
37,692-F _~g_
_. -- - i : '..
-1g-
depleted in hydrogen is obtained on the high pressure
side of the membrane which is removed from the high
pressure side of the membrane as non-permeate.
This invention is a process for separating
hydrogen from gas mixtures containing gases such as
nitrogen, carbon monoxide, carbon dioxide and light
hydrocarbons in addition to hydrogen. The process
comprises contacting a Feed gas stream containing
hydrogen with the membrane hereinbefore described
under conditions such that hydrogen selectively
permeates through the membrane in comparison to the
other components. As used herein, the term light
hydrocarbons refers to gaseous saturated and
unsaturated C1-~ hydrocarbons. The process is carried
out at pressures and temperatures which do not
deleteriously affect the membranes. Preferably, the
pressure on the high pressure side of the membrane is
between 35 psig (241 kPa) and 2000 psig (13,780 kPa),
more preferably between 100 psig (689 kPa) and 1000
psig (6890 kPa). The pressure differential across the
membrane is preferably between 15 psig (103 kPa) and
1500 psig (10,335 kPa), and more preferably between 50
psig (344 kPa) and 500 psig (3,445 kPa). The
temperature at which the feed gas stream is contacted
with the membrane is preferably between 0 and 150°C,
more preferably between 5 and 100°C. In one preferred
embodiment, the membrane is in a hollow Fiber form.
In the embodiment wherein the membrane is in hollow
fiber form, the feed gas T,ixture may be introduced on
the outside or inside of the hollow Fiber.
37,692-F -19-
~20m ~ - ~...
Gas permeability is defined as
(amount of permeate)(membrane thickness)
p= _______________________________________________
(area)(time)(driving force across the membrane)
A standard permeability measurement unit is the Barrer
(Ba), which is equal to
~~0 (centimeter3 (STP)) (centimeter)
___________ ________________________
10 (eentimeter)2 (second) (centimeter Hg)
em3(STP) cm
abbreviated hereinafter as 10"10 -__ ________
cm2~s cm Hg
The reduced flux is defined as (permeability) .
(membrane thickness). A standard reduced flux unit is
_6 (centimeter)3 (STP)
i0 ____ _______ __________________________
(centimeter)2-(second) (centimeter Hg)
abbreviated hereinafter as
~6 em3 (STP)
10 ~m2-S-em-Hg__ ,
The separation factor or selectivity of a membrane is
defined as the ratio of the permeability or Flux of the
faster permeating gas to the permeability or flux of the
slower permeating gas.
The membranes useful in this invention for
hydrogen/light hydrocarbon separation preferably possess
a separation factor for hydrogen/light hydrocarbons at
25°C of at least 25, more preferably of at least 50.
The membranes useful in this invention for
37,692-F -20-
!.; ; , >-; .
-21-
hydrogen/nitrogen separation preferably possess a
separation factor for hydrogen/nitrogen at 25°C of at
least 15, more preferably of at least 40.
The membranes useful in this invention
preferably have a reduced flux for hydrogen of at
least 10-5cm3(STP)/(cm2sec emHg) or greater, more
preferably of 10-~ em3(STP)/(em2sec cmHg) or greater.
The membrane preferably possesses a permeability for
hydrogen of at least 5 Ba, more preferably of at least
10 Ba. The membrane separation process of this
invention may be combined with non-membrane separation
processes such as cryogenics (low temperature
distillation) and pressure swing adsorption.
The following Examples are included f.or
illustrative purposes only and are not intended to
limit the scope of the Claims or the invention.
,-Example 1 - Tetrabromobisphenol A Polycarbonate
L' ~ 1 ... T .. .. 4 ...
A solution containing 18 weight percent
tetrabromobisphenol A polycarbonate (TBBA-PC) in
diehloromethane is prepared. The solution is cast
onto a glass plate and the solvent allowed to
evaporate for 1 hour. The film is removed from the
glass plate. Excess solvent is allowed to evaporate
from the membrane at atmospheric conditions overnight.
Subsequently, the film is placed in a vacuum oven at
120 to 140°C for at least 3 days to remove residual
solvent. The film is 0.16 millimeters thick.
A disc of 1.5 inch (3.8 em) diameter is cut
from the film and placed in a eonstant-
37,692-F -21-
-22-
volume/variable-pressure gas permeation test
apparatus. For details regarding this permeability
measurement technique, see Pye, Hoehn, and Panar,
"Measurement of Gas Permeability of Polymers, I.
Permeabilities in Constant-Volume/Uariable-Pressure
Apparatus," Journal of Applied Polymer Science, Vol.
20, 1976, pp. 1921-1931. Pure gas at a pressure of
100 psig (690 kPa g) and 35°C are fed to one side of
the film and the amount of gas permeating through the
membrane measured. Se aration factor and
p permeability
data are reported in Table I.
20
30
37,692-F -22-
_ r: ; r
~' '; i,,
-23- ..
Table I
SINGLE GAS TESTING OF TBBA-PC FILM
Gas Flux Separation Factor
em2 STP)
em2 s emHg
H~ H2/CH~ H2/C2H~ H2/C2H6
16.3 150 108 380
Example 2 - Tetrabromobisphenol A Polyoarbonate Hollow
Fiber Tests
Hollow fibers are extruded from an extrusion
blend containing 52.0 weight percent
tetrabromobisphenol A polycarbonate (TBBA-PC), 32.6
weight percent N-methylpyrrolidinone, and 15.1 weight
percent tetraethylene glycol as described in O.S.
Patent 24,772,392. The fibers are fabricated into test
units and the single gas permeabilities measured- at- a
feed pressure of 50 psig (345 kPa g) and a temperature
of 35°C. Data are reported in Table II.
30
37,692-F -23-
-24-
Table II
SINGLE GAS TESTING OF TBBA-PC FIBERS
Ga Flux
cm~ (STP) Separation Faetor
cm2 s emH
g
H H2/CH4 H2/C2H4 H2/C2H6
2
12.9 120 53 194
Example 3 - Tetrabromobisphenol A Polvearbonate
Annealed Hollow Fiber Tests
Hollow fibers of TBBA-PC are extruded as
described in Example 2. The fibers are annealed at
90°C for 4 days. Single gas fluxes are measured at a
feed pressure of 50 psig (345 kPa g) and a temperature
ofw50°C. Data are shown in Table III. Annealing
increases the gas separation factor significantly
while decreasing the gas flux.
Table III
Ga Flux
em~ (STP) Separation Factor
cm2 s cmH
g
H H2/CH4 H2/C2H4 H2/C2H6H2/N2
2
unannealed 104.4 60.9 205.9 83.8
22.2 x 10-5
annealed 114.2 73.2 433.6 106.3
7.11 x 10-5
37,692-F -24-
-25-
Example 4 - Tetrabromobisphenol A Polycarbonate Hollow
Fiber Temperature Dependence Tests
Hollow fibers of TBBA-PC are extruded as
described in Example 2. The fibers are annealed at
90°C for ~4 days. Single gas fluxes are measured at a
feed pressure of 50 psig (345 kPa g) and a temperature
of 15, 35, 50 and 80°C, respectively, Data are shown
in Table IV.
15
25
35
37,692-F _25_
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